Add support for using multiple hugepage sizes simultaneously
on mainline. Currently, support for 256M has been added which
can be used along with 8M pages.

Page tables are set like this (e.g. for 256M page):
    VA + (8M * x) -> PA + (8M * x) (sz bit = 256M) where x in [0, 31]

and TSB is set similarly:
    VA + (4M * x) -> PA + (4M * x) (sz bit = 256M) where x in [0, 63]

- Testing

Tested on Sonoma (which supports 256M pages) by running stream
benchmark instances in parallel: one instance uses 8M pages and
another uses 256M pages, consuming 48G each.

Boot params used:

default_hugepagesz=256M hugepagesz=256M hugepages=300 hugepagesz=8M
hugepages=10000
Signed-off-by: NNitin Gupta <nitin.m.gupta@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

On panic, all other CPUs are stopped except the one which had
hit panic. To keep console alive, we need to migrate hvcons irq
to panicked CPU.
Signed-off-by: NVijay Kumar <vijay.ac.kumar@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

CPU needs to be marked offline before stopping it. When not marked
offline, the xcall receives HV_EWOULDBLOCK and so assumes that not all
CPUs received the message, and retries. After 10000 retries, it finally
fails with fatal mondo timeout.
Signed-off-by: NVijay Kumar <vijay.ac.kumar@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

When returning from the user probe code into userspace process, PC & NPC are
truncated to 32 bits.

Due to shared libraries getting loaded very high in the virtual address
space of
the process, placing a user probe inside a shared library makes the kernel
return into the process at the wrong address, causing it to seg'fault
most of
the time.

This patch prevents truncating PC and NPC.
Signed-off-by: NEric Saint Etienne <eric.saint.etienne@oracle.com>
Reviewed-by: NDavid Aldridge <david.j.aldridge@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

We currently define macros referring to cpu_data if CONFIG_SMP is
defined, but only include the declaration if CONFIG_NUMA is defined.

Fixes: 541cc394 ("sparc: fix a building error reported by kbuild")
Signed-off-by: NBen Hutchings <ben@decadent.org.uk>
Acked-by: NGonglei <arei.gonglei@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The objects viking_ops, viking_sun4d_smp_ops and smp_cachetlb_ops of
type sparc32_cachetlb_ops are not modified anywhere after getting modified
in the init functions. Inside init their reference is also stored in a
pointer of type const struct sparc32_cachetlb_ops *. So these structures
are never modified after init, therefore add __ro_after to the declaration
of these structures.
Signed-off-by: NBhumika Goyal <bhumirks@gmail.com>
Reviewed-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

show_mem() allows to filter out node specific data which is irrelevant
to the allocation request via SHOW_MEM_FILTER_NODES.  The filtering is
done in skip_free_areas_node which skips all nodes which are not in the
mems_allowed of the current process.  This works most of the time as
expected because the nodemask shouldn't be outside of the allocating
task but there are some exceptions.  E.g.  memory hotplug might want to
request allocations from outside of the allowed nodes (see
new_node_page).

Get rid of this hardcoded behavior and push the allocation mask down the
show_mem path and use it instead of cpuset_current_mems_allowed.  NULL
nodemask is interpreted as cpuset_current_mems_allowed.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170117091543.25850-5-mhocko@kernel.orgSigned-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NMel Gorman <mgorman@suse.de>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We have a generic implementation for quite some time already.  If there
is any arch specific information to be printed then we should add a
callback called from the generic code rather than duplicate the whole
show_mem.

The current code has resulted in the code duplication and the output
divergence which is both confusing and adds maintainance costs.

Let's just get rid of this mess.

Link: http://lkml.kernel.org/r/20170117091543.25850-4-mhocko@kernel.orgSigned-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: Guan Xuetao <gxt@mprc.pku.edu.cn> [UniCore32]
Acked-by: Helge Deller <deller@gmx.de> [for parisc]
Acked-by: Chris Metcalf <cmetcalf@mellanox.com> [for tile]
Acked-by: NMel Gorman <mgorman@suse.de>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

cputime_t is now only used by two architectures:

	* powerpc (when CONFIG_VIRT_CPU_ACCOUNTING_NATIVE=y)
	* s390

And since the core doesn't use it anymore, we don't need any arch support
from the others. So we can remove their stub implementations.

A final cleanup would be to provide an efficient pure arch
implementation of cputime_to_nsec() for s390 and powerpc and finally
remove include/linux/cputime.h .
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Link: http://lkml.kernel.org/r/1485832191-26889-36-git-send-email-fweisbec@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

User processes trying to access an invalid memory address via PIO will
receive a SIGBUS signal instead of causing a panic.  Memory errors will
receive a SIGKILL since a SIGBUS may result in a coredump which may
attempt to repeat the faulting access.
Signed-off-by: NLiam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Error queues use a non-zero first word to detect if the queues are full.
Using pages that have not been zeroed may result in false positive
overflow events.  These queues are set up once during boot so zeroing
all mondo and error queue pages is safe.

Note that the false positive overflow does not always occur because the
page allocation for these queues is so early in the boot cycle that
higher number CPUs get fresh pages.  It is only when traps are serviced
with lower number CPUs who were given already used pages that this issue
is exposed.
Signed-off-by: NLiam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This file was using module.h for search_exception_table.  We've
now separated that content out into its own file "extable.h" so
now move over to that.  Unlike most other instances, we can't
delete the module.h include here since the file needs that for
the within_module_init definition.
Reported-by: Nkbuild test robot <lkp@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>

Relax ordering(RO) is one feature of 82599 NIC, to enable this feature can
enhance the performance for some cpu architecure, such as SPARC and so on.
Currently it only supports one special cpu architecture(SPARC) in 82599
driver to enable RO feature, this is not very common for other cpu architecture
which really needs RO feature.
This patch add one common config CONFIG_ARCH_WANT_RELAX_ORDER to set RO feature,
and should define CONFIG_ARCH_WANT_RELAX_ORDER in sparc Kconfig firstly.
Signed-off-by: NMao Wenan <maowenan@huawei.com>
Reviewed-by: NAlexander Duyck <alexander.duyck@gmail.com>
Reviewed-by: NAlexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NTom Hromatka <tom.hromatka@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Use symbolic names MM_TSB_BASE and MM_TSB_HUGE instead of numeric values
0 and 1 in __tsb_context_switch.  Code cleanup only, no functional change.
Suggested-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NMike Kravetz <mike.kravetz@oracle.com>
Acked-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

There is no point in having an extra type for extra confusion. u64 is
unambiguous.

Conversion was done with the following coccinelle script:

@rem@
@@
-typedef u64 cycle_t;

@fix@
typedef cycle_t;
@@
-cycle_t
+u64
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: John Stultz <john.stultz@linaro.org>

This was entirely automated, using the script by Al:

  PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*<asm/uaccess.h>'
  sed -i -e "s!$PATT!#include <linux/uaccess.h>!" \
        $(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h)

to do the replacement at the end of the merge window.
Requested-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Implement functions watchdog_nmi_enable and watchdog_nmi_disable to
enable/disable nmi watchdog.  Sparc uses arch specific nmi watchdog
handler.  Currently, we do not have a way to enable/disable nmi watchdog
dynamically.  With these patches we can enable or disable arch specific
nmi watchdogs using proc or sysctl interface.

Example commands.
To enable: echo 1 >  /proc/sys/kernel/nmi_watchdog
To disable: echo 0 >  /proc/sys/kernel/nmi_watchdog

It can also achieved using the sysctl parameter kernel.nmi_watchdog

Link: http://lkml.kernel.org/r/1478034826-43888-4-git-send-email-babu.moger@oracle.comSigned-off-by: NBabu Moger <babu.moger@oracle.com>
Acked-by: NDon Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Josh Hunt <johunt@akamai.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This change allows us to pass DMA_ATTR_SKIP_CPU_SYNC which allows us to
avoid invoking cache line invalidation if the driver will just handle it
via a sync_for_cpu or sync_for_device call.

Link: http://lkml.kernel.org/r/20161110113544.76501.40008.stgit@ahduyck-blue-test.jf.intel.comSigned-off-by: NAlexander Duyck <alexander.h.duyck@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

>> arch/sparc/include/asm/topology_64.h:44:44:
error: implicit declaration of function 'cpu_data'
[-Werror=implicit-function-declaration]

 #define topology_physical_package_id(cpu) (cpu_data(cpu).proc_id)
                                               ^
Let's include cpudata.h in topology_64.h.

Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Suggested-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Acked-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

It really has to be pgdp, not pgd.

It just happend to work since all callers have 'pgd' as an argument.
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

There are some error paths where we should restore IRQs but we don't.

Fixes: bb620c3d ("sparc: Make sparc64 use scalable lib/iommu-common.c functions")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The original code causes a static checker warning because it has a
continue inside a do { } while (0); loop.  In that context, a continue
and a break are equivalent.  The intent was to go back to the start of
the loop so the continue was a bug.

I've added a retry label at the start and changed the continue to a goto
retry.  Then I removed the do { } while (0) loop and pulled the code in
one indent level.

Fixes: 2791c1a4 ("SPARC/LEON: added support for selecting Timer Core and Timer within core")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

My static checker complains that if "lvl" is ULONG_MAX (this is 64 bit)
then some of the strings will overflow.  I don't know if that's possible
but it seems simple enough to make the buffers slightly larger.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

We shouldn't dereference "iommu" until after we have checked that it is
non-NULL.

Fixes: f08978b0 ("sparc64: Enable sun4v dma ops to use IOMMU v2 APIs")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Use builtin_platform_driver() helper to simplify the code.
Signed-off-by: NGeliang Tang <geliangtang@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NEric Saint Etienne <eric.saint.etienne@oracle.com>
Signed-off-by: NAllen Pais <allen.pais@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This patch exports the sender chronograph stats via the socket
SO_TIMESTAMPING channel. Currently we can instrument how long a
particular application unit of data was queued in TCP by tracking
SOF_TIMESTAMPING_TX_SOFTWARE and SOF_TIMESTAMPING_TX_SCHED. Having
these sender chronograph stats exported simultaneously along with
these timestamps allow further breaking down the various sender
limitation.  For example, a video server can tell if a particular
chunk of video on a connection takes a long time to deliver because
TCP was experiencing small receive window. It is not possible to
tell before this patch without packet traces.

To prepare these stats, the user needs to set
SOF_TIMESTAMPING_OPT_STATS and SOF_TIMESTAMPING_OPT_TSONLY flags
while requesting other SOF_TIMESTAMPING TX timestamps. When the
timestamps are available in the error queue, the stats are returned
in a separate control message of type SCM_TIMESTAMPING_OPT_STATS,
in a list of TLVs (struct nlattr) of types: TCP_NLA_BUSY_TIME,
TCP_NLA_RWND_LIMITED, TCP_NLA_SNDBUF_LIMITED. Unit is microsecond.
Signed-off-by: NFrancis Yan <francisyyan@gmail.com>
Signed-off-by: NYuchung Cheng <ycheng@google.com>
Signed-off-by: NSoheil Hassas Yeganeh <soheil@google.com>
Acked-by: NNeal Cardwell <ncardwell@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Install the callbacks via the state machine and let the core invoke
the callbacks on the already online CPUs.

The previous convention of keeping the files around until the CPU is dead
has not been preserved as there is no point to keep them available when the
cpu is going down. This makes the hotplug call symmetric.
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: N"David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Cc: rt@linuxtronix.de
Link: http://lkml.kernel.org/r/20161117183541.8588-18-bigeasy@linutronix.deSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

Drop duplicate header scatterlist.h from iommu_common.h.
Signed-off-by: NGeliang Tang <geliangtang@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This new config parameter limits the space used for "Lock debugging:
prove locking correctness" by about 4MB. The current sparc systems have
the limitation of 32MB size for kernel size including .text, .data and
.bss sections. With PROVE_LOCKING feature, the kernel size could grow
beyond this limit and causing system boot-up issues. With this option,
kernel limits the size of the entries of lock_chains, stack_trace etc.,
so that kernel fits in required size limit. This is not visible to user
and only used for sparc.
Signed-off-by: NBabu Moger <babu.moger@oracle.com>
Acked-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

ATU 64bit addressing allows PCIe devices with 64bit DMA capabilities
to use ATU for 64bit DMA.
Signed-off-by: NTushar Dave <tushar.n.dave@oracle.com>
Reviewed-by: Nchris hyser <chris.hyser@oracle.com>
Acked-by: NSowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Add Hypervisor IOMMU v2 APIs pci_iotsb_map(), pci_iotsb_demap() and
enable sun4v dma ops to use IOMMU v2 API for all PCIe devices with
64bit DMA mask.
Signed-off-by: NTushar Dave <tushar.n.dave@oracle.com>
Reviewed-by: Nchris hyser <chris.hyser@oracle.com>
Acked-by: NSowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

In order to use Hypervisor (HV) IOMMU v2 API for map/demap, each PCIe
device has to be bound to IOTSB using HV API pci_iotsb_bind().
Signed-off-by: NTushar Dave <tushar.n.dave@oracle.com>
Reviewed-by: Nchris hyser <chris.hyser@oracle.com>
Acked-by: NSowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Like legacy IOMMU, use common iommu_map_table and iommu_pool for ATU.
This change initializes iommu_map_table and iommu_pool for ATU.
Signed-off-by: NTushar Dave <tushar.n.dave@oracle.com>
Reviewed-by: Nchris hyser <chris.hyser@oracle.com>
Reviewed-by: NSowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

ATU (Address Translation Unit) is a new IOMMU in SPARC supported with
Hypervisor IOMMU v2 APIs.

Current SPARC IOMMU supports only 32bit address ranges and one TSB
per PCIe root complex that has a 2GB per root complex DVMA space
limit. The limit has become a scalability bottleneck nowadays that
a typical 10G/40G NIC can consume 300MB-500MB DVMA space per
instance. When DVMA resource is exhausted, devices will not be usable
since the driver can't allocate DVMA.

ATU removes bottleneck by allowing guest os to create IOTSB of size
32G (or more) with 64bit address ranges available in ATU HW. 32G is
more than enough DVMA space to be shared by all PCIe devices under
root complex contrast to 2G space provided by legacy IOMMU.

ATU allows PCIe devices to use 64bit DMA addressing. Devices
which choose to use 32bit DMA mask will continue to work with the
existing legacy IOMMU.
Signed-off-by: NTushar Dave <tushar.n.dave@oracle.com>
Reviewed-by: Nchris hyser <chris.hyser@oracle.com>
Acked-by: NSowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

This change allows ATU (new IOMMU) in SPARC systems to request
large (32M) contiguous memory during boot for creating IOTSB backing
store.
Signed-off-by: NDave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: NTushar Dave <tushar.n.dave@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

No need to duplicate the same define everywhere. Since
the only user is stop-machine and the only provider is
s390, we can use a default implementation of cpu_relax_yield()
in sched.h.
Suggested-by: NRussell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Acked-by: NRussell King <rmk+kernel@armlinux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Noam Camus <noamc@ezchip.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: kvm@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-s390 <linux-s390@vger.kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: sparclinux@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1479298985-191589-1-git-send-email-borntraeger@de.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

As there are no users left, we can remove cpu_relax_lowlatency()
implementations from every architecture.
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Noam Camus <noamc@ezchip.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Cc: <linux-arch@vger.kernel.org>
Link: http://lkml.kernel.org/r/1477386195-32736-6-git-send-email-borntraeger@de.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

For spinning loops people do often use barrier() or cpu_relax().
For most architectures cpu_relax and barrier are the same, but on
some architectures cpu_relax can add some latency.
For example on power,sparc64 and arc, cpu_relax can shift the CPU
towards other hardware threads in an SMT environment.
On s390 cpu_relax does even more, it uses an hypercall to the
hypervisor to give up the timeslice.
In contrast to the SMT yielding this can result in larger latencies.
In some places this latency is unwanted, so another variant
"cpu_relax_lowlatency" was introduced. Before this is used in more
and more places, lets revert the logic and provide a cpu_relax_yield
that can be called in places where yielding is more important than
latency. By default this is the same as cpu_relax on all architectures.
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Noam Camus <noamc@ezchip.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1477386195-32736-2-git-send-email-borntraeger@de.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>