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Date:   Fri, 10 Nov 2017 14:08:04 +0800
From:   kemi <kemi.wang@...el.com>
To:     Andrew Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>
Cc:     Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [01/18] x86/asm/64: Remove the restore_c_regs_and_iret label

Some performance regression/improvement is reported by LKP-tools for this patch series
tested with Intel Atom processor. So, post the data here for your reference.

Branch:x86/entry_consolidation
Commit id:
     base:50da9d439392fdd91601d36e7f05728265bff262
     head:69af865668fdb86a95e4e948b1f48b2689d60b73
Benchmark suite:will-it-scale
Download link:https://github.com/antonblanchard/will-it-scale/tree/master/tests
Metrics:
     will-it-scale.per_process_ops=processes/nr_cpu
     will-it-scale.per_thread_ops=threads/nr_cpu

tbox:lkp-avoton3(nr_cpu=8,memory=16G)
CPU: Intel(R) Atom(TM) CPU  C2750  @ 2.40GHz
Performance regression with will-it-scale benchmark suite:
testcase        base            change          head            metric                   
eventfd1        1505677         -5.9%           1416132         will-it-scale.per_process_ops
                1352716         -3.0%           1311943         will-it-scale.per_thread_ops
lseek2          7306698         -4.3%           6991473         will-it-scale.per_process_ops
                4906388         -3.6%           4730531         will-it-scale.per_thread_ops
lseek1          7355365         -4.2%           7046224         will-it-scale.per_process_ops
                4928961         -3.7%           4748791         will-it-scale.per_thread_ops
getppid1        8479806         -4.1%           8129026         will-it-scale.per_process_ops
                8515252         -4.1%           8162076         will-it-scale.per_thread_ops
lock1           1054249         -3.2%           1020895         will-it-scale.per_process_ops
                989145          -2.6%           963578          will-it-scale.per_thread_ops
dup1            2675825         -3.0%           2596257         will-it-scale.per_process_ops
futex3          4986520         -2.8%           4846640         will-it-scale.per_process_ops
                5009388         -2.7%           4875126         will-it-scale.per_thread_ops
futex4          3932936         -2.0%           3854240         will-it-scale.per_process_ops
                3950138         -2.0%           3872615         will-it-scale.per_thread_ops
futex1          2941886         -1.8%           2888912         will-it-scale.per_process_ops
futex2          2500203         -1.6%           2461065         will-it-scale.per_process_ops
                1534692         -2.3%           1499532         will-it-scale.per_thread_ops
malloc1         61314           -1.0%           60725           will-it-scale.per_process_ops
                19996           -1.5%           19688           will-it-scale.per_thread_ops

Performance improvement with will-it-scale benchmark suite:
testcase        base            change          head            metric                   
context_switch1 176376          +1.6%           179152          will-it-scale.per_process_ops
                180703          +1.9%           184209          will-it-scale.per_thread_ops
page_fault2     179716          +2.5%           184272          will-it-scale.per_process_ops
                146890          +2.8%           150989          will-it-scale.per_thread_ops
page_fault3     666953          +3.7%           691735          will-it-scale.per_process_ops
                464641          +5.0%           487952          will-it-scale.per_thread_ops
unix1           483094          +4.4%           504201          will-it-scale.per_process_ops
                450055          +7.5%           483637          will-it-scale.per_thread_ops
read2           575887          +5.0%           604440          will-it-scale.per_process_ops
                500319          +5.2%           526361          will-it-scale.per_thread_ops
poll1           4614597         +5.4%           4864022         will-it-scale.per_process_ops
                3981551         +5.8%           4213409         will-it-scale.per_thread_ops
pwrite2         383344          +5.7%           405151          will-it-scale.per_process_ops
                367006          +5.0%           385209          will-it-scale.per_thread_ops
sched_yield     3011191         +6.0%           3191710         will-it-scale.per_process_ops
                3024171         +6.1%           3208197         will-it-scale.per_thread_ops
pipe1           755487          +6.2%           802622          will-it-scale.per_process_ops
                705136          +8.8%           766950          will-it-scale.per_thread_ops
pwrite3         422850          +6.6%           450660          will-it-scale.per_process_ops
                413370          +3.7%           428704          will-it-scale.per_thread_ops
readseek1       972102          +6.7%           1036852         will-it-scale.per_process_ops
                844877          +6.6%           900686          will-it-scale.per_thread_ops
pwrite1         981310          +6.8%           1047809         will-it-scale.per_process_ops
                944421          +5.7%           998472          will-it-scale.per_thread_ops
pread2          444743          +6.9%           475332          will-it-scale.per_process_ops
                430299          +6.1%           456718          will-it-scale.per_thread_ops
writeseek1      849520          +7.0%           908672          will-it-scale.per_process_ops
                746978          +9.3%           816372          will-it-scale.per_thread_ops
pread3          1108949         +7.2%           1189021         will-it-scale.per_process_ops
                1088521         +5.5%           1148522         will-it-scale.per_thread_ops
mmap1           207314          +7.3%           222442          will-it-scale.per_process_ops
                82533           +6.9%           88199           will-it-scale.per_thread_ops
writeseek3      377973          +7.4%           405853          will-it-scale.per_process_ops
                333156          +11.4%          371100          will-it-scale.per_thread_ops
open2           266217          +7.6%           286335          will-it-scale.per_process_ops
                208208          +6.6%           222052          will-it-scale.per_thread_ops
unlink2         54774           +7.7%           59013           will-it-scale.per_process_ops
                53792           +7.0%           57584           will-it-scale.per_thread_ops
poll2           257458          +8.0%           278072          will-it-scale.per_process_ops
                153400          +8.4%           166256          will-it-scale.per_thread_ops
posix_semaphore1 19898603        +8.3%           21552049        will-it-scale.per_process_ops
                19797092        +8.4%           21458395        will-it-scale.per_thread_ops
pthread_mutex2  35871102        +8.4%           38868017        will-it-scale.per_process_ops
                21506625        +8.4%           23312550        will-it-scale.per_thread_ops
mmap2           154242          +8.5%           167348          will-it-scale.per_process_ops
                62234           +7.4%           66841           will-it-scale.per_thread_ops
unlink1         31487           +9.3%           34404           will-it-scale.per_process_ops
                31607           +8.5%           34285           will-it-scale.per_thread_ops
open1           280301          +9.9%           307995          will-it-scale.per_process_ops
                213863          +7.8%           230585          will-it-scale.per_thread_ops
signal1         355247          +11.2%          394875          will-it-scale.per_process_ops
                176973          +9.7%           194160          will-it-scale.per_thread_ops

============================================================================================
Branch:x86/entry_consolidation
Commit id:
     base:50da9d439392fdd91601d36e7f05728265bff262
     head:69af865668fdb86a95e4e948b1f48b2689d60b73
Benchmark suite:unixbench
Download link:https://github.com/kdlucas/byte-unixbench.git

tbox:lkp-avoton2(nr_cpu=8,memory=16G)
CPU: Intel(R) Atom(TM) CPU  C2750  @ 2.40GHz
Performance regression with unixbench benchmark suite:
testcase        base            change          head            metric                   
syscall         1206            -4.2%           1155            unixbench.score          
pipe            4851            -1.5%           4779            unixbench.score          
execl           498.83          -1.2%           492.90          unixbench.score          

Performance improvement with unixbench benchmark suite:
testcase        base            change          head            metric                   
fsdisk          2150            +2.7%           2208            unixbench.score

=============================================================================================

On 2017年10月26日 16:26, Andrew Lutomirski wrote:
> The only user was the 64-bit opportunistic SYSRET failure path, and
> that path didn't really need it.  This change makes the
> opportunistic SYSRET code a bit more straightforward and gets rid of
> the label.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> Reviewed-by: Borislav Petkov <bp@...e.de>
> ---
>  arch/x86/entry/entry_64.S | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 49167258d587..afe1f403fa0e 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -245,7 +245,6 @@ entry_SYSCALL64_slow_path:
>  	call	do_syscall_64		/* returns with IRQs disabled */
>  
>  return_from_SYSCALL_64:
> -	RESTORE_EXTRA_REGS
>  	TRACE_IRQS_IRETQ		/* we're about to change IF */
>  
>  	/*
> @@ -314,6 +313,7 @@ return_from_SYSCALL_64:
>  	 */
>  syscall_return_via_sysret:
>  	/* rcx and r11 are already restored (see code above) */
> +	RESTORE_EXTRA_REGS
>  	RESTORE_C_REGS_EXCEPT_RCX_R11
>  	movq	RSP(%rsp), %rsp
>  	UNWIND_HINT_EMPTY
> @@ -321,7 +321,7 @@ syscall_return_via_sysret:
>  
>  opportunistic_sysret_failed:
>  	SWAPGS
> -	jmp	restore_c_regs_and_iret
> +	jmp	restore_regs_and_iret
>  END(entry_SYSCALL_64)
>  
>  ENTRY(stub_ptregs_64)
> @@ -638,7 +638,6 @@ retint_kernel:
>   */
>  GLOBAL(restore_regs_and_iret)
>  	RESTORE_EXTRA_REGS
> -restore_c_regs_and_iret:
>  	RESTORE_C_REGS
>  	REMOVE_PT_GPREGS_FROM_STACK 8
>  	INTERRUPT_RETURN
> 

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