svn commit: r305545 - head/sys/arm64/arm64

[Andrew Turner]

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() &&