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  1. 17 3月, 2017 1 次提交
  3. 31 10月, 2016 2 次提交
  5. 26 10月, 2016 1 次提交
  7. 25 10月, 2016 1 次提交
  9. 27 9月, 2016 1 次提交
  11. 16 9月, 2016 1 次提交
    • R
      tcg: Merge GETPC and GETRA · 01ecaf43
      由 Richard Henderson 提交于 
      The return address argument to the softmmu template helpers was
confused.  In the legacy case, we wanted to indicate that there
is no return address, and so passed in NULL.  However, we then
immediately subtracted GETPC_ADJ from NULL, resulting in a non-zero
value, indicating the presence of an (invalid) return address.

Push the GETPC_ADJ subtraction down to the only point it's required:
immediately before use within cpu_restore_state_from_tb, after all
NULL pointer checks have been completed.

This makes GETPC and GETRA identical.  Remove GETRA as the lesser
used macro, replacing all uses with GETPC.
Signed-off-by: NRichard Henderson <rth@twiddle.net>
      01ecaf43
  13. 14 9月, 2016 1 次提交
  15. 27 7月, 2016 1 次提交
  17. 12 7月, 2016 2 次提交
  19. 12 6月, 2016 1 次提交
    • E
      tb hash: track translated blocks with qht · 909eaac9
      由 Emilio G. Cota 提交于 
      Having a fixed-size hash table for keeping track of all translation blocks
is suboptimal: some workloads are just too big or too small to get maximum
performance from the hash table. The MRU promotion policy helps improve
performance when the hash table is a little undersized, but it cannot
make up for severely undersized hash tables.

Furthermore, frequent MRU promotions result in writes that are a scalability
bottleneck. For scalability, lookups should only perform reads, not writes.
This is not a big deal for now, but it will become one once MTTCG matures.

The appended fixes these issues by using qht as the implementation of
the TB hash table. This solution is superior to other alternatives considered,
namely:

- master: implementation in QEMU before this patchset
- xxhash: before this patch, i.e. fixed buckets + xxhash hashing + MRU.
- xxhash-rcu: fixed buckets + xxhash + RCU list + MRU.
              MRU is implemented here by adding an intermediate struct
              that contains the u32 hash and a pointer to the TB; this
              allows us, on an MRU promotion, to copy said struct (that is not
              at the head), and put this new copy at the head. After a grace
              period, the original non-head struct can be eliminated, and
              after another grace period, freed.
- qht-fixed-nomru: fixed buckets + xxhash + qht without auto-resize +
                   no MRU for lookups; MRU for inserts.
The appended solution is the following:
- qht-dyn-nomru: dynamic number of buckets + xxhash + qht w/ auto-resize +
                 no MRU for lookups; MRU for inserts.

The plots below compare the considered solutions. The Y axis shows the
boot time (in seconds) of a debian jessie image with arm-softmmu; the X axis
sweeps the number of buckets (or initial number of buckets for qht-autoresize).
The plots in PNG format (and with errorbars) can be seen here:
  http://imgur.com/a/Awgnq

Each test runs 5 times, and the entire QEMU process is pinned to a
single core for repeatability of results.

                            Host: Intel Xeon E5-2690

  28 ++------------+-------------+-------------+-------------+------------++
     A*****        +             +             +             master **A*** +
  27 ++    *                                                 xxhash ##B###++
     |      A******A******                               xxhash-rcu $$C$$$ |
  26 C$$                  A******A******            qht-fixed-nomru*%%D%%%++
     D%%$$                              A******A******A*qht-dyn-mru A*E****A
  25 ++ %%$$                                          qht-dyn-nomru &&F&&&++
     B#####%                                                               |
  24 ++    #C$$$$$                                                        ++
     |      B###  $                                                        |
     |          ## C$$$$$$                                                 |
  23 ++           #       C$$$$$$                                         ++
     |             B######       C$$$$$$                                %%%D
  22 ++                  %B######       C$$$$$$C$$$$$$C$$$$$$C$$$$$$C$$$$$$C
     |                    D%%%%%%B######      @E@@@@@@    %%%D%%%@@@E@@@@@@E
  21 E@@@@@@E@@@@@@F&&&@@@E@@@&&&D%%%%%%B######B######B######B######B######B
     +             E@@@   F&&&   +      E@     +      F&&&   +             +
  20 ++------------+-------------+-------------+-------------+------------++
     14            16            18            20            22            24
                             log2 number of buckets

                                 Host: Intel i7-4790K

  14.5 ++------------+------------+-------------+------------+------------++
       A**           +            +             +            master **A*** +
    14 ++ **                                                 xxhash ##B###++
  13.5 ++   **                                           xxhash-rcu $$C$$$++
       |                                            qht-fixed-nomru %%D%%% |
    13 ++     A******                                   qht-dyn-mru @@E@@@++
       |             A*****A******A******             qht-dyn-nomru &&F&&& |
  12.5 C$$                               A******A******A*****A******    ***A
    12 ++ $$                                                        A***  ++
       D%%% $$                                                             |
  11.5 ++  %%                                                             ++
       B###  %C$$$$$$                                                      |
    11 ++  ## D%%%%% C$$$$$                                               ++
       |     #      %      C$$$$$$                                         |
  10.5 F&&&&&&B######D%%%%%       C$$$$$$C$$$$$$C$$$$$$C$$$$$C$$$$$$    $$$C
    10 E@@@@@@E@@@@@@B#####B######B######E@@@@@@E@@@%%%D%%%%%D%%%###B######B
       +             F&&          D%%%%%%B######B######B#####B###@@@D%%%   +
   9.5 ++------------+------------+-------------+------------+------------++
       14            16           18            20           22            24
                              log2 number of buckets

Note that the original point before this patch series is X=15 for "master";
the little sensitivity to the increased number of buckets is due to the
poor hashing function in master.

xxhash-rcu has significant overhead due to the constant churn of allocating
and deallocating intermediate structs for implementing MRU. An alternative
would be do consider failed lookups as "maybe not there", and then
acquire the external lock (tb_lock in this case) to really confirm that
there was indeed a failed lookup. This, however, would not be enough
to implement dynamic resizing--this is more complex: see
"Resizable, Scalable, Concurrent Hash Tables via Relativistic
Programming" by Triplett, McKenney and Walpole. This solution was
discarded due to the very coarse RCU read critical sections that we have
in MTTCG; resizing requires waiting for readers after every pointer update,
and resizes require many pointer updates, so this would quickly become
prohibitive.

qht-fixed-nomru shows that MRU promotion is advisable for undersized
hash tables.

However, qht-dyn-mru shows that MRU promotion is not important if the
hash table is properly sized: there is virtually no difference in
performance between qht-dyn-nomru and qht-dyn-mru.

Before this patch, we're at X=15 on "xxhash"; after this patch, we're at
X=15 @ qht-dyn-nomru. This patch thus matches the best performance that we
can achieve with optimum sizing of the hash table, while keeping the hash
table scalable for readers.

The improvement we get before and after this patch for booting debian jessie
with arm-softmmu is:

- Intel Xeon E5-2690: 10.5% less time
- Intel i7-4790K: 5.2% less time

We could get this same improvement _for this particular workload_ by
statically increasing the size of the hash table. But this would hurt
workloads that do not need a large hash table. The dynamic (upward)
resizing allows us to start small and enlarge the hash table as needed.

A quick note on downsizing: the table is resized back to 2**15 buckets
on every tb_flush; this makes sense because it is not guaranteed that the
table will reach the same number of TBs later on (e.g. most bootup code is
thrown away after boot); it makes sense to grow the hash table as
more code blocks are translated. This also avoids the complication of
having to build downsizing hysteresis logic into qht.
Reviewed-by: NSergey Fedorov <serge.fedorov@linaro.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1465412133-3029-15-git-send-email-cota@braap.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>
      909eaac9
  21. 09 6月, 2016 1 次提交
  23. 19 5月, 2016 2 次提交
  25. 13 5月, 2016 10 次提交
  27. 23 3月, 2016 2 次提交
  29. 21 1月, 2016 6 次提交
  31. 10 11月, 2015 1 次提交
  33. 05 11月, 2015 1 次提交
  35. 13 10月, 2015 2 次提交
    • P
      exec: remove non-TCG stuff from exec-all.h header. · 88401cbc
      由 Paolo Bonzini 提交于 
      The header is included from basically everywhere, thanks to cpu.h.
It should be moved to the (TCG only) files that actually need it.
As a start, remove non-TCG stuff.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
      88401cbc
    • P
      exec.c: Collect AddressSpace related fields into a CPUAddressSpace struct · 32857f4d
      由 Peter Maydell 提交于 
      Gather up all the fields currently in CPUState which deal with the CPU's
AddressSpace into a separate CPUAddressSpace struct. This paves the way
for allowing the CPU to know about more than one AddressSpace.

The rearrangement also allows us to make the MemoryListener a directly
embedded object in the CPUAddressSpace (it could not be embedded in
CPUState because 'struct MemoryListener' isn't defined for the user-only
builds). This allows us to resolve the FIXME in tcg_commit() by going
directly from the MemoryListener to the CPUAddressSpace.

This patch extracts the actual update of the cached dispatch pointer
from cpu_reload_memory_map() (which is renamed accordingly to
cpu_reloading_memory_map() as it is only responsible for breaking
cpu-exec.c's RCU critical section now). This lets us keep the definition
of the CPUAddressSpace struct private to exec.c.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-Id: <1443709790-25180-4-git-send-email-peter.maydell@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
      32857f4d
  37. 07 10月, 2015 3 次提交