Author: andrew
Date: Wed Sep 7 16:22:05 2016
New Revision: 305545
URL: https://svnweb.freebsd.org/changeset/base/305545
Log:
Only call cpu_icache_sync_range when inserting an executable page. If the
page is non-executable the contents of the i-cache are unimportant so this
call is just adding unneeded overhead when inserting pages.
While doing research using gem5 with an O3 pipeline and 1k/32k/1M iTLB/L1
iCache/L2 Bjoern Zeeb (bz@) observed a fairly high rate of calls into
arm64_icache_sync_range() from pmap_enter() along with a high number of
instruction fetches and iTLB/iCache hits.
Limiting the calls to arm64_icache_sync_range() to only executable pages,
we observe the iTLB and iCache Hit going down by about 43%. These numbers
are quite misleading when looked at alone as at the same time instructions
retired were reduced by 19.2% and instruction fetches were reduced by 38.8%.
Overall this reduced the runtime of the test program by 22.4%.
On Juno hardware, in steady-state, running the same test, using the cycle
count to determine runtime, we do see a reduction of up to 28.9% in runtime.
While these numbers certainly depend on the program executed, we expect an
overall performance improvement.
Reported by: bz
Obtained from: ABT Systems Ltd
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Modified:
head/sys/arm64/arm64/pmap.c
Modified: head/sys/arm64/arm64/pmap.c
==============================================================================
--- head/sys/arm64/arm64/pmap.c Wed Sep 7 16:19:20 2016 (r305544)
+++ head/sys/arm64/arm64/pmap.c Wed Sep 7 16:22:05 2016 (r305545)
@@ -2939,8 +2939,9 @@ validate:
pmap_invalidate_page(pmap, va);
if (pmap != pmap_kernel()) {
- if (pmap == &curproc->p_vmspace->vm_pmap)
- cpu_icache_sync_range(va, PAGE_SIZE);
+ if (pmap == &curproc->p_vmspace->vm_pmap &&
+ (prot & VM_PROT_EXECUTE) != 0)
+ cpu_icache_sync_range(va, PAGE_SIZE);
if ((mpte == NULL || mpte->wire_count == NL3PG) &&
pmap_superpages_enabled() &&
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