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From: Andi Kleen <ak@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Yi Sun <yi.sun@intel.com>,
	dave.hansen@intel.com, linux-kernel@vger.kernel.org,
	x86@kernel.org, sohil.mehta@intel.com,
	ilpo.jarvinen@linux.intel.com, heng.su@intel.com,
	tony.luck@intel.com, yi.sun@linux.intel.com, yu.c.chen@intel.com
Subject: Re: [PATCH v7 1/3] x86/fpu: Measure the Latency of XSAVE and XRSTOR
Date: Thu, 21 Sep 2023 09:52:36 -0700	[thread overview]
Message-ID: <ZQx01AfyvbJQYPsi@tassilo> (raw)
In-Reply-To: <ZQvqvpSbyub6gFZX@gmail.com>

> It seems unnecessarily complex: why does it have to measure latency 
> directly? Tracepoints *by default* come with event timestamps. A latency 
> measurement tool should be able to subtract two timestamps to extract the 
> latency between two tracepoints...
> 
> In fact, function tracing is enabled on all major Linux distros:
> 
>   kepler:~/tip> grep FUNCTION_TRACER /boot/config-6.2.0-33-generic 
>   CONFIG_HAVE_FUNCTION_TRACER=y
>   CONFIG_FUNCTION_TRACER=y
> 
> Why not just enable function tracing for the affected FPU context switching 
> functions?

Or use PT address filters to get it even accurately, as described
in [1]. In any case I agree the trace points are not needed.

-Andi

[1] https://lore.kernel.org/lkml/ZPOIVmC6aY9GBtdJ@tassilo/

  parent reply	other threads:[~2023-09-21 18:54 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-21  6:28 [PATCH v7 0/3] x86/fpu Measure the Latency of XSAVES and XRSTORS Yi Sun
2023-09-21  6:28 ` [PATCH v7 1/3] x86/fpu: Measure the Latency of XSAVE and XRSTOR Yi Sun
2023-09-21  7:03   ` Ingo Molnar
2023-09-21  8:24     ` Yi Sun
2023-09-21 16:52     ` Andi Kleen [this message]
2023-09-22  3:44       ` Yi Sun
2023-09-21  6:28 ` [PATCH v7 2/3] tools/testing/fpu: Add script to consume trace log of xsave latency Yi Sun
2023-09-21  6:29 ` [PATCH v7 3/3] tools/testing/fpu: Add a 'count' column Yi Sun

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