From bb4093deb259ea9c92415796a6a139e35272f8a8 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Thu, 16 Dec 2010 17:03:15 -0600 Subject: [PATCH] lguest: restore boot speed lguest is dumb and drops *all* the pagetables for set_pte (which is only used for kernel mapping manipulation, so it's OK without highmem). But it's used a lot in boot, too. As a guest optimization, we suppressed this flushing until the first page switch. Now we have initial_page_table, that happens much earlier, so extend the heuristic to wait until we switch to something other than the swapper_pg_dir or initial_page_table. As measured on my laptop under kvm, this dropped the time-to-mount-root from 48 seconds to 4.3 seconds. Signed-off-by: Rusty Russell --- arch/x86/lguest/boot.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c index 45e64b37b237..24e49737df7a 100644 --- a/arch/x86/lguest/boot.c +++ b/arch/x86/lguest/boot.c @@ -531,7 +531,10 @@ static void lguest_write_cr3(unsigned long cr3) { lguest_data.pgdir = cr3; lazy_hcall1(LHCALL_NEW_PGTABLE, cr3); - cr3_changed = true; + + /* These two page tables are simple, linear, and used during boot */ + if (cr3 != __pa(swapper_pg_dir) && cr3 != __pa(initial_page_table)) + cr3_changed = true; } static unsigned long lguest_read_cr3(void) @@ -703,9 +706,9 @@ static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval) * to forget all of them. Fortunately, this is very rare. * * ... except in early boot when the kernel sets up the initial pagetables, - * which makes booting astonishingly slow: 1.83 seconds! So we don't even tell - * the Host anything changed until we've done the first page table switch, - * which brings boot back to 0.25 seconds. + * which makes booting astonishingly slow: 48 seconds! So we don't even tell + * the Host anything changed until we've done the first real page table switch, + * which brings boot back to 4.3 seconds. */ static void lguest_set_pte(pte_t *ptep, pte_t pteval) { -- GitLab