aboutsummaryrefslogtreecommitdiffstats
path: root/arch/x86/lguest
diff options
context:
space:
mode:
authorRusty Russell <rusty@rustcorp.com.au>2010-12-16 17:03:15 -0600
committerRusty Russell <rusty@rustcorp.com.au>2010-12-16 17:03:15 +1030
commitbb4093deb259ea9c92415796a6a139e35272f8a8 (patch)
tree806e7be7f7194d91e9135bc2f6af64a5ca2fdd7b /arch/x86/lguest
parentbb6f1d9a99f1947d91693de62ed54ac3bf1e2dfe (diff)
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/x86/lguest')
-rw-r--r--arch/x86/lguest/boot.c11
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)
{

Privacy Policy