The patch titled
lguest: pin stack page optimization
has been added to the -mm tree. Its filename is
lguest-the-host-code-lgko-pin-stack-page-optimization.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: lguest: pin stack page optimization
From: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
We make sure that the stack is always mapped in pin_stack_pages by simply
calling demand_page, but that calls get_user_pages() to find the pfn, which is
way overkill since the page is almost certainly already mapped. So don't call
pin_stack_pages every context switch (unless genuinely a completely clean
context, all the kernel mappings are kept in sync), and when we do call it,
have it check if it needs to call demand_page().
This speeds guest context switch by 25%:
Before:
Time for one context switch via pipe: 10606 nsec
After:
Time for one context switch via pipe: 7805 nsec
Native:
Time for one context switch via pipe: 4701 nsec
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/i386/lguest/page_tables.c | 31 +++++++++++++++++++++++++------
1 file changed, 25 insertions(+), 6 deletions(-)
diff -puN arch/i386/lguest/page_tables.c~lguest-the-host-code-lgko-pin-stack-page-optimization arch/i386/lguest/page_tables.c
--- a/arch/i386/lguest/page_tables.c~lguest-the-host-code-lgko-pin-stack-page-optimization
+++ a/arch/i386/lguest/page_tables.c
@@ -155,14 +155,29 @@ int demand_page(struct lguest *lg, u32 v
return page_in(lg, vaddr, (write ? _PAGE_DIRTY : 0)|_PAGE_ACCESSED);
}
+/* This is much faster than the full demand_page logic. */
+static int page_writable(struct lguest *lg, unsigned long vaddr)
+{
+ u32 *top, *pte;
+
+ top = toplev(lg, lg->pgdidx, vaddr);
+ if (!(*top & _PAGE_PRESENT))
+ return 0;
+
+ pte = pteof(lg, *top, vaddr);
+ return (*pte & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
+}
+
void pin_stack_pages(struct lguest *lg)
{
unsigned int i;
u32 stack = lg->state->tss.esp1;
- for (i = 0; i < lg->stack_pages; i++)
- if (!demand_page(lg, stack - i*PAGE_SIZE, 1))
+ for (i = 0; i < lg->stack_pages; i++) {
+ if (!page_writable(lg, stack - i * PAGE_SIZE)
+ && !demand_page(lg, stack - i * PAGE_SIZE, 1))
kill_guest(lg, "bad stack page %i@%#x", i, stack);
+ }
}
static unsigned int find_pgdir(struct lguest *lg, u32 pgtable)
@@ -198,7 +213,7 @@ void guest_pagetable_flush_user(struct l
flush_user_mappings(lg, lg->pgdidx);
}
-static unsigned int new_pgdir(struct lguest *lg, u32 cr3)
+static unsigned int new_pgdir(struct lguest *lg, u32 cr3, int *blank_pgdir)
{
unsigned int next;
@@ -207,6 +222,9 @@ static unsigned int new_pgdir(struct lgu
lg->pgdirs[next].pgdir = (u32 *)get_zeroed_page(GFP_KERNEL);
if (!lg->pgdirs[next].pgdir)
next = lg->pgdidx;
+ else
+ /* There are no mappings: you'll need to re-pin */
+ *blank_pgdir = 1;
}
lg->pgdirs[next].cr3 = cr3;
/* Release all the non-kernel mappings. */
@@ -217,14 +235,15 @@ static unsigned int new_pgdir(struct lgu
void guest_new_pagetable(struct lguest *lg, u32 pgtable)
{
- int newpgdir;
+ int newpgdir, repin = 0;
newpgdir = find_pgdir(lg, pgtable);
if (newpgdir == ARRAY_SIZE(lg->pgdirs))
- newpgdir = new_pgdir(lg, pgtable);
+ newpgdir = new_pgdir(lg, pgtable, &repin);
lg->pgdidx = newpgdir;
lg->cr3 = __pa(lg->pgdirs[lg->pgdidx].pgdir);
- pin_stack_pages(lg);
+ if (repin)
+ pin_stack_pages(lg);
}
static void release_all_pagetables(struct lguest *lg)
_
Patches currently in -mm which might be from rusty@xxxxxxxxxxxxxxx are
futex-restartable-futex_wait.patch
i386-vdso_prelink-warning-fix.patch
cleanup-initialize-esp0-properly-all-the-time.patch
lguest-preparation-export_symbol_gpl-5-functions.patch
lguest-preparation-expose-futex-infrastructure.patch
lguest-kconfig-and-headers.patch
lguest-the-host-code-lgko.patch
lguest-the-host-code-lgko-cleanup-allocate-separate-pages-for-switcher-code.patch
lguest-the-host-code-lgko-cleanup-clean-up-regs-save-restore.patch
lguest-the-host-code-lgko-pin-stack-page-optimization.patch
lguest-guest-code.patch
lguest-makefile.patch
lguest-trivial-guest-network-driver.patch
lguest-trivial-guest-console-driver.patch
lguest-trivial-guest-block-driver.patch
lguest-trivial-guest-block-driver-lguest-block-device-speedup.patch
lguest-documentatation-and-example-launcher.patch
lguest-documentatation-and-example-launcher-bridging-support-in-example-code.patch
lguest-documentatation-and-example-launcher-bridging-support-in-example-codelguest-documentation-fixes.patch
lguest-use-read-only-pages-rather-than-segments-to-protect-high-mapped-switcher.patch
lguest-optimize-away-copy-in-and-out-of-per-cpu-guest-pages.patch
lguest-dont-crash-host-on-nmi.patch
module-use-krealloc.patch
extend-print_symbol-capability.patch
array_size-check-for-type.patch
____call_usermodehelper-dont-flush_signals.patch
add-ability-to-keep-track-of-callers-of-symbol_getput.patch
add-ability-to-keep-track-of-callers-of-symbol_getput-tidy.patch
update-mtd-use-of-symbol_getput.patch
update-dvb-use-of-symbol_getput.patch
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