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From: Anton Blanchard <anton@samba.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, paulus@samba.org
Subject: Re: [PATCH] powerpc/mm: Add trace point for tracking hash pte fault
Date: Tue, 3 Feb 2015 09:01:29 +1100	[thread overview]
Message-ID: <20150203090129.5e3c7494@kryten> (raw)
In-Reply-To: <87vbjk707w.fsf@linux.vnet.ibm.com>

Hi Aneesh,

> yes. We do use jump label. I also verified that looking at .s
> 
> #APP
>  # 23 "./arch/powerpc/include/asm/jump_label.h" 1
>         1:
>         nop
>         .pushsection __jump_table,  "aw"
>         .llong 1b, .L201, __tracepoint_hash_fault+8      #,
>         .popsection
> 
>  # 0 "" 2

So we insert a single nop, and the slow path is in another section. I'd
be surprised if we could measure this, unless the nop causes a branch
target alignment issue the slow path caused some hot path icache layout
issues.

> Without patch
> sys: 0m11.2425
> 
> With patch:
> sys: 0m11.3258
>
> ie, a -0.7% impact 
> 
> If that impact is high we could possibly put that tracepoint within
> #ifdef CONFIG_DEBUG_VM ?

Did the real time change? I'd be careful about comparing based on
system time.

My feeling is we should not hide it behind CONFIG_DEBUG_VM.

Anton

  reply	other threads:[~2015-02-02 22:01 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-20 11:35 [PATCH] powerpc/mm: Add trace point for tracking hash pte fault Aneesh Kumar K.V
2015-01-21  3:07 ` Michael Ellerman
2015-01-21  8:45   ` Aneesh Kumar K.V
2015-01-28  6:11     ` Michael Ellerman
2015-02-02 10:26       ` Anton Blanchard
2015-02-02 16:21         ` Aneesh Kumar K.V
2015-02-02 22:01           ` Anton Blanchard [this message]
2015-02-03  3:07             ` Aneesh Kumar K.V
2015-02-02 16:12       ` Aneesh Kumar K.V
2015-04-02  8:44         ` Aneesh Kumar K.V

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