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Message-ID: <20110307104423.GA3661@jolsa.redhat.com> Date: Mon, 7 Mar 2011 11:44:23 +0100 From: Jiri Olsa <jolsa@...hat.com> To: Ingo Molnar <mingo@...e.hu> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>, Frédéric Weisbecker <fweisbec@...il.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, masami.hiramatsu.pt@...achi.com, hpa@...or.com, ananth@...ibm.com, davem@...emloft.net, linux-kernel@...r.kernel.org, tglx@...utronix.de, eric.dumazet@...il.com, 2nddept-manager@....hitachi.co.jp Subject: Re: [PATCH 1/2] x86: separating entry text section hi, any feedback? thanks, jirka On Tue, Feb 22, 2011 at 01:52:01PM +0100, Jiri Olsa wrote: > On Tue, Feb 22, 2011 at 09:09:34AM +0100, Ingo Molnar wrote: > > > > * Jiri Olsa <jolsa@...hat.com> wrote: > > > > > Putting x86 entry code to the separate section: .entry.text. > > > > Trying to apply your patch i noticed one detail: > > > > > before patch: > > > 26282174 L1-icache-load-misses ( +- 0.099% ) (scaled from 81.00%) > > > 0.206651959 seconds time elapsed ( +- 0.152% ) > > > > > > after patch: > > > 24237651 L1-icache-load-misses ( +- 0.117% ) (scaled from 80.96%) > > > 0.210509948 seconds time elapsed ( +- 0.140% ) > > > > So time elapsed actually went up. > > > > hackbench is notoriously unstable when it comes to runtime - and increasing the > > --repeat value only has limited effects on that. > > > > Dropping all system caches: > > > > echo 1 > /proc/sys/vm/drop_caches > > > > Seems to do a better job of 'resetting' system state, but if we put that into the > > measured workload then the results are all over the place (as we now depend on IO > > being done): > > > > # cat hb10 > > > > echo 1 > /proc/sys/vm/drop_caches > > ./hackbench 10 > > > > # perf stat --repeat 3 ./hb10 > > > > Time: 0.097 > > Time: 0.095 > > Time: 0.101 > > > > Performance counter stats for './hb10' (3 runs): > > > > 21.351257 task-clock-msecs # 0.044 CPUs ( +- 27.165% ) > > 6 context-switches # 0.000 M/sec ( +- 34.694% ) > > 1 CPU-migrations # 0.000 M/sec ( +- 25.000% ) > > 410 page-faults # 0.019 M/sec ( +- 0.081% ) > > 25,407,650 cycles # 1189.984 M/sec ( +- 49.154% ) > > 25,407,650 instructions # 1.000 IPC ( +- 49.154% ) > > 5,126,580 branches # 240.107 M/sec ( +- 46.012% ) > > 192,272 branch-misses # 3.750 % ( +- 44.911% ) > > 901,701 cache-references # 42.232 M/sec ( +- 12.857% ) > > 802,767 cache-misses # 37.598 M/sec ( +- 9.282% ) > > > > 0.483297792 seconds time elapsed ( +- 31.152% ) > > > > So here's a perf stat feature suggestion to solve such measurement problems: a new > > 'pre-run' 'dry' command could be specified that is executed before the real 'hot' > > run is executed. Something like this: > > > > perf stat --pre-run-script ./hb10 --repeat 10 ./hackbench 10 > > > > Would do the cache-clearing before each run, it would run hackbench once (dry run) > > and then would run hackbench 10 for real - and would repeat the whole thing 10 > > times. Only the 'hot' portion of the run would be measured and displayed in the perf > > stat output event counts. > > > > Another observation: > > > > > 24237651 L1-icache-load-misses ( +- 0.117% ) (scaled from 80.96%) > > > > Could you please do runs that do not display 'scaled from' messages? Since we are > > measuring a relatively small effect here, and scaling adds noise, it would be nice > > to ensure that the effect persists with non-scaled events as well: > > > > You can do that by reducing the number of events that are measured. The PMU can not > > measure all those L1 cache events you listed - so only use the most important one > > and add cycles and instructions to make sure the measurements are comparable: > > > > -e L1-icache-load-misses -e instructions -e cycles > > > > Btw., there's another 'perf stat' feature suggestion: it would be nice if it was > > possible to 'record' a perf stat run, and do a 'perf diff' over it. That would > > compare the two runs all automatically, without you having to do the comparison > > manually. > > hi, > > I made another test with "reseting" the system state as suggested and > only for cache-misses together with instructions and cycles events. > > I can see even bigger drop of icache load misses than before > from 19359739 to 16448709 (about 15%). > > The instruction/cycles count is slightly bigger in the patched > kernel run though.. > > perf stat --repeat 100 -e L1-icache-load-misses -e instructions -e cycles ./hackbench/hackbench 10 > > ------------------------------------------------------------------------------- > before patch: > > Performance counter stats for './hackbench/hackbench 10' (100 runs): > > 19359739 L1-icache-load-misses ( +- 0.313% ) > 2667528936 instructions # 0.498 IPC ( +- 0.165% ) > 5352849800 cycles ( +- 0.303% ) > > 0.205402048 seconds time elapsed ( +- 0.299% ) > > Performance counter stats for './hackbench/hackbench 10' (500 runs): > > 19417627 L1-icache-load-misses ( +- 0.147% ) > 2676914223 instructions # 0.497 IPC ( +- 0.079% ) > 5389516026 cycles ( +- 0.144% ) > > 0.206267711 seconds time elapsed ( +- 0.138% ) > > > ------------------------------------------------------------------------------- > after patch: > > Performance counter stats for './hackbench/hackbench 10' (100 runs): > > 16448709 L1-icache-load-misses ( +- 0.426% ) > 2698406306 instructions # 0.500 IPC ( +- 0.177% ) > 5393976267 cycles ( +- 0.321% ) > > 0.206072845 seconds time elapsed ( +- 0.276% ) > > Performance counter stats for './hackbench/hackbench 10' (500 runs): > > 16490788 L1-icache-load-misses ( +- 0.180% ) > 2717734941 instructions # 0.502 IPC ( +- 0.079% ) > 5414756975 cycles ( +- 0.148% ) > > 0.206747566 seconds time elapsed ( +- 0.137% ) > > > Attaching patch with above numbers in comment. > > thanks, > jirka > > > --- > Putting x86 entry code to the separate section: .entry.text. > > Separating the entry text section seems to have performance > benefits with regards to the instruction cache usage. > > Running hackbench showed that the change compresses the icache > footprint. The icache load miss rate went down by about 15%: > > before patch: > 19417627 L1-icache-load-misses ( +- 0.147% ) > > after patch: > 16490788 L1-icache-load-misses ( +- 0.180% ) > > > Whole perf output follows. > > - results for current tip tree: > Performance counter stats for './hackbench/hackbench 10' (500 runs): > > 19417627 L1-icache-load-misses ( +- 0.147% ) > 2676914223 instructions # 0.497 IPC ( +- 0.079% ) > 5389516026 cycles ( +- 0.144% ) > > 0.206267711 seconds time elapsed ( +- 0.138% ) > > - results for current tip tree with the patch applied are: > Performance counter stats for './hackbench/hackbench 10' (500 runs): > > 16490788 L1-icache-load-misses ( +- 0.180% ) > 2717734941 instructions # 0.502 IPC ( +- 0.079% ) > 5414756975 cycles ( +- 0.148% ) > > 0.206747566 seconds time elapsed ( +- 0.137% ) > > > wbr, > jirka > > > Signed-off-by: Jiri Olsa <jolsa@...hat.com> > --- > arch/x86/ia32/ia32entry.S | 2 ++ > arch/x86/kernel/entry_32.S | 6 ++++-- > arch/x86/kernel/entry_64.S | 6 ++++-- > arch/x86/kernel/vmlinux.lds.S | 1 + > include/asm-generic/sections.h | 1 + > include/asm-generic/vmlinux.lds.h | 6 ++++++ > 6 files changed, 18 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S > index 0ed7896..50f1630 100644 > --- a/arch/x86/ia32/ia32entry.S > +++ b/arch/x86/ia32/ia32entry.S > @@ -25,6 +25,8 @@ > #define sysretl_audit ia32_ret_from_sys_call > #endif > > + .section .entry.text, "ax" > + > #define IA32_NR_syscalls ((ia32_syscall_end - ia32_sys_call_table)/8) > > .macro IA32_ARG_FIXUP noebp=0 > diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S > index c8b4efa..f5accf8 100644 > --- a/arch/x86/kernel/entry_32.S > +++ b/arch/x86/kernel/entry_32.S > @@ -65,6 +65,8 @@ > #define sysexit_audit syscall_exit_work > #endif > > + .section .entry.text, "ax" > + > /* > * We use macros for low-level operations which need to be overridden > * for paravirtualization. The following will never clobber any registers: > @@ -788,7 +790,7 @@ ENDPROC(ptregs_clone) > */ > .section .init.rodata,"a" > ENTRY(interrupt) > -.text > +.section .entry.text, "ax" > .p2align 5 > .p2align CONFIG_X86_L1_CACHE_SHIFT > ENTRY(irq_entries_start) > @@ -807,7 +809,7 @@ vector=FIRST_EXTERNAL_VECTOR > .endif > .previous > .long 1b > - .text > + .section .entry.text, "ax" > vector=vector+1 > .endif > .endr > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > index 891268c..39f8d21 100644 > --- a/arch/x86/kernel/entry_64.S > +++ b/arch/x86/kernel/entry_64.S > @@ -61,6 +61,8 @@ > #define __AUDIT_ARCH_LE 0x40000000 > > .code64 > + .section .entry.text, "ax" > + > #ifdef CONFIG_FUNCTION_TRACER > #ifdef CONFIG_DYNAMIC_FTRACE > ENTRY(mcount) > @@ -744,7 +746,7 @@ END(stub_rt_sigreturn) > */ > .section .init.rodata,"a" > ENTRY(interrupt) > - .text > + .section .entry.text > .p2align 5 > .p2align CONFIG_X86_L1_CACHE_SHIFT > ENTRY(irq_entries_start) > @@ -763,7 +765,7 @@ vector=FIRST_EXTERNAL_VECTOR > .endif > .previous > .quad 1b > - .text > + .section .entry.text > vector=vector+1 > .endif > .endr > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S > index e70cc3d..459dce2 100644 > --- a/arch/x86/kernel/vmlinux.lds.S > +++ b/arch/x86/kernel/vmlinux.lds.S > @@ -105,6 +105,7 @@ SECTIONS > SCHED_TEXT > LOCK_TEXT > KPROBES_TEXT > + ENTRY_TEXT > IRQENTRY_TEXT > *(.fixup) > *(.gnu.warning) > diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h > index b3bfabc..c1a1216 100644 > --- a/include/asm-generic/sections.h > +++ b/include/asm-generic/sections.h > @@ -11,6 +11,7 @@ extern char _sinittext[], _einittext[]; > extern char _end[]; > extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[]; > extern char __kprobes_text_start[], __kprobes_text_end[]; > +extern char __entry_text_start[], __entry_text_end[]; > extern char __initdata_begin[], __initdata_end[]; > extern char __start_rodata[], __end_rodata[]; > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index fe77e33..906c3ce 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -424,6 +424,12 @@ > *(.kprobes.text) \ > VMLINUX_SYMBOL(__kprobes_text_end) = .; > > +#define ENTRY_TEXT \ > + ALIGN_FUNCTION(); \ > + VMLINUX_SYMBOL(__entry_text_start) = .; \ > + *(.entry.text) \ > + VMLINUX_SYMBOL(__entry_text_end) = .; > + > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > #define IRQENTRY_TEXT \ > ALIGN_FUNCTION(); \ > -- > 1.7.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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