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| author | Rusty Russell <rusty@rustcorp.com.au> | 2010-12-17 02:03:15 +0300 |
|---|---|---|
| committer | Rusty Russell <rusty@rustcorp.com.au> | 2010-12-16 09:33:15 +0300 |
| commit | bb4093deb259ea9c92415796a6a139e35272f8a8 (patch) | |
| tree | 806e7be7f7194d91e9135bc2f6af64a5ca2fdd7b /arch | |
| parent | bb6f1d9a99f1947d91693de62ed54ac3bf1e2dfe (diff) | |
| download | linux-bb4093deb259ea9c92415796a6a139e35272f8a8.tar.xz | |
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 <rusty@rustcorp.com.au>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/lguest/boot.c | 11 |
1 files 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) { |