x86: Optimize clear_page()

Currently, we CALL clear_page() which then JMPs to the proper function chosen by the alternatives. What we should do instead is CALL the proper function directly. (This was something Ingo suggested a while ago). So let's do that. Measuring our favourite kernel build workload shows that there are no significant changes in performance. AMD === --- /tmp/before 2017-02-09 18:01:46.451961188 +0100 +++ /tmp/after 2017-02-09 18:01:54.883961175 +0100 @@ -1,15 +1,15 @@ Performance counter stats for 'system wide' (5 runs): - 1028960.373643 cpu-clock (msec) # 6.000 CPUs utilized ( +- 1.41% ) + 1023086.018961 cpu-clock (msec) # 6.000 CPUs utilized ( +- 1.20% ) - 518,744 context-switches # 0.504 K/sec ( +- 1.04% ) + 518,254 context-switches # 0.507 K/sec ( +- 1.01% ) - 38,112 cpu-migrations # 0.037 K/sec ( +- 1.95% ) + 37,917 cpu-migrations # 0.037 K/sec ( +- 1.02% ) - 20,874,266 page-faults # 0.020 M/sec ( +- 0.07% ) + 20,918,897 page-faults # 0.020 M/sec ( +- 0.18% ) - 2,043,646,230,667 cycles # 1.986 GHz ( +- 0.14% ) (66.67%) + 2,045,305,584,032 cycles # 1.999 GHz ( +- 0.16% ) (66.67%) - 553,698,855,431 stalled-cycles-frontend # 27.09% frontend cycles idle ( +- 0.07% ) (66.67%) + 555,099,401,413 stalled-cycles-frontend # 27.14% frontend cycles idle ( +- 0.13% ) (66.67%) - 621,544,286,390 stalled-cycles-backend # 30.41% backend cycles idle ( +- 0.39% ) (66.67%) + 621,371,430,254 stalled-cycles-backend # 30.38% backend cycles idle ( +- 0.32% ) (66.67%) - 1,738,364,431,659 instructions # 0.85 insn per cycle + 1,739,895,771,901 instructions # 0.85 insn per cycle - # 0.36 stalled cycles per insn ( +- 0.11% ) (66.67%) + # 0.36 stalled cycles per insn ( +- 0.13% ) (66.67%) - 391,170,943,850 branches # 380.161 M/sec ( +- 0.13% ) (66.67%) + 391,398,551,757 branches # 382.567 M/sec ( +- 0.13% ) (66.67%) - 22,567,810,411 branch-misses # 5.77% of all branches ( +- 0.11% ) (66.67%) + 22,574,726,683 branch-misses # 5.77% of all branches ( +- 0.13% ) (66.67%) - 171.480741921 seconds time elapsed ( +- 1.41% ) + 170.509229451 seconds time elapsed ( +- 1.20% ) Intel ===== --- /tmp/before 2017-02-09 20:36:19.851947473 +0100 +++ /tmp/after 2017-02-09 20:36:30.151947458 +0100 @@ -1,15 +1,15 @@ Performance counter stats for 'system wide' (5 runs): - 2207248.598126 cpu-clock (msec) # 8.000 CPUs utilized ( +- 0.69% ) + 2213300.106631 cpu-clock (msec) # 8.000 CPUs utilized ( +- 0.73% ) - 899,342 context-switches # 0.407 K/sec ( +- 0.68% ) + 898,381 context-switches # 0.406 K/sec ( +- 0.79% ) - 80,553 cpu-migrations # 0.036 K/sec ( +- 1.13% ) + 80,979 cpu-migrations # 0.037 K/sec ( +- 1.11% ) - 36,171,148 page-faults # 0.016 M/sec ( +- 0.02% ) + 36,179,791 page-faults # 0.016 M/sec ( +- 0.02% ) - 6,665,288,826,484 cycles # 3.020 GHz ( +- 0.07% ) (83.33%) + 6,671,638,410,799 cycles # 3.014 GHz ( +- 0.06% ) (83.33%) - 5,065,975,115,197 stalled-cycles-frontend # 76.01% frontend cycles idle ( +- 0.11% ) (83.33%) + 5,076,835,183,223 stalled-cycles-frontend # 76.10% frontend cycles idle ( +- 0.11% ) (83.33%) - 3,841,556,350,614 stalled-cycles-backend # 57.64% backend cycles idle ( +- 0.13% ) (66.67%) + 3,852,823,974,333 stalled-cycles-backend # 57.75% backend cycles idle ( +- 0.12% ) (66.67%) - 4,148,398,171,079 instructions # 0.62 insn per cycle + 4,148,997,156,059 instructions # 0.62 insn per cycle - # 1.22 stalled cycles per insn ( +- 0.10% ) (83.33%) + # 1.22 stalled cycles per insn ( +- 0.11% ) (83.33%) - 887,187,118,591 branches # 401.943 M/sec ( +- 0.09% ) (83.33%) + 887,271,341,121 branches # 400.882 M/sec ( +- 0.11% ) (83.33%) - 30,139,439,034 branch-misses # 3.40% of all branches ( +- 0.09% ) (83.33%) + 30,134,864,997 branch-misses # 3.40% of all branches ( +- 0.06% ) (83.33%) - 275.904405540 seconds time elapsed ( +- 0.69% ) + 276.660352016 seconds time elapsed ( +- 0.73% ) allmodconfig vmlinux size grows by a ~1Kb but that's fine - we optimize our calling of the clear_page variants. text data bss dec hex filename 9051979 23067670 27009024 59128673 3863b61 vmlinux 9053000 23067670 27009024 59129694 3863f5e vmlinux.clear_page Signed-off-by: Borislav Petkov <bp@suse.de>
0day-ci · Feb 9, 2017 · 0ad07c8104eb5c12dfcb86581c1cc657183496cc · 0ad07c8
1 parent 10b9dd5
commit 0ad07c8104eb5c12dfcb86581c1cc657183496cc
Show file tree

Hide file tree

Showing 3 changed files with 37 additions and 11 deletions.
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
@@ -226,6 +226,23 @@ static inline int alternatives_text_reserved(void *start, void *end)
 		  [new2] "i" (newfunc2), ## input);			      \
 }
 
+/*
+ * Like alternative_call, but there are two features and respective functions.
+ * If CPU has feature2, function2 is used.
+ * Otherwise, if CPU has feature1, function1 is used.
+ * Otherwise, old function is used.
+ */
+#define alternative_void_call_2(oldfunc, newfunc1, feature1, newfunc2,		\
+				feature2, input...)				\
+{										\
+	register void *__sp asm(_ASM_SP);					\
+	asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,	\
+		"call %P[new2]", feature2)					\
+		: "+r" (__sp)							\
+		: [old] "i" (oldfunc), [new1] "i" (newfunc1),			\
+		  [new2] "i" (newfunc2), ## input);				\
+}
+
 /*
  * use this macro(s) if you need more than one output parameter
  * in alternative_io

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
@@ -4,6 +4,7 @@
 #include <asm/page_64_types.h>
 
 #ifndef __ASSEMBLY__
+#include <asm/alternative.h>
 
 /* duplicated to the one in bootmem.h */
 extern unsigned long max_pfn;
@@ -34,7 +35,18 @@ extern unsigned long __phys_addr_symbol(unsigned long);
 #define pfn_valid(pfn)          ((pfn) < max_pfn)
 #endif
 
-void clear_page(void *page);
+void clear_page_orig(void *page);
+void clear_page_rep(void *page);
+void clear_page_erms(void *page);
+
+static inline void clear_page(void *page)
+{
+	alternative_void_call_2(clear_page_orig,
+				clear_page_rep, X86_FEATURE_REP_GOOD,
+				clear_page_erms, X86_FEATURE_ERMS,
+				"D" (page));
+}
+
 void copy_page(void *to, void *from);
 
 #endif	/* !__ASSEMBLY__ */

diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S
@@ -14,20 +14,15 @@
  * Zero a page.
  * %rdi	- page
  */
-ENTRY(clear_page)
-
-	ALTERNATIVE_2 "jmp clear_page_orig", "", X86_FEATURE_REP_GOOD, \
-		      "jmp clear_page_c_e", X86_FEATURE_ERMS
-
+ENTRY(clear_page_rep)
 	movl $4096/8,%ecx
 	xorl %eax,%eax
 	rep stosq
 	ret
-ENDPROC(clear_page)
-EXPORT_SYMBOL(clear_page)
+ENDPROC(clear_page_rep)
+EXPORT_SYMBOL_GPL(clear_page_rep)
 
 ENTRY(clear_page_orig)
-
 	xorl   %eax,%eax
 	movl   $4096/64,%ecx
 	.p2align 4
@@ -47,10 +42,12 @@ ENTRY(clear_page_orig)
 	nop
 	ret
 ENDPROC(clear_page_orig)
+EXPORT_SYMBOL_GPL(clear_page_orig)
 
-ENTRY(clear_page_c_e)
+ENTRY(clear_page_erms)
 	movl $4096,%ecx
 	xorl %eax,%eax
 	rep stosb
 	ret
-ENDPROC(clear_page_c_e)
+ENDPROC(clear_page_erms)
+EXPORT_SYMBOL_GPL(clear_page_erms)