From: Andi Kleen <ak@linux.intel.com>
To: David Laight <David.Laight@aculab.com>
Cc: 'Aubrey Li' <aubrey.li@intel.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
"dave.hansen@intel.com" <dave.hansen@intel.com>,
"arjan@linux.intel.com" <arjan@linux.intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Aubrey Li <aubrey.li@linux.intel.com>
Subject: Re: [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks
Date: Wed, 12 Dec 2018 10:00:46 -0800 [thread overview]
Message-ID: <20181212180046.GG25620@tassilo.jf.intel.com> (raw)
In-Reply-To: <c87224bd48bc4296a38ae4852bf28071@AcuMS.aculab.com>
> Isn't a thread likely to clear the AVX registers at the end of a function
> that uses them.
> In particular this removes the massive overhead on certain cpus of
> switching between two AVX modes.
> So it is actually unlikely that XSAVE will need to save them at all?
Only if context switches only happened on function boundaries, which
is obviously not the case.
Yes the detection mechanism is not 100% accurate, but if AVX
is used significantly it should eventually detect it.
Think of it as a statistical sampling heuristic.
>
> As I've also said before the registers are caller saved and since
> systems calls are normal function calls the application code
> would have to save them across a system call.
> This allows the kernel to zero the registers on system call entry
> again meaning that XSAVE won't normally have to save them.
While I agree this would be nice, the Linux system call ABI
wasn't defined like this, so it cannot be done at this point.
-Andi
prev parent reply other threads:[~2018-12-12 18:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-11 0:24 [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks Aubrey Li
2018-12-11 0:24 ` [PATCH v4 2/2] proc: add AVX-512 usage to /proc/pid/status Aubrey Li
2018-12-11 17:57 ` Tim Chen
2018-12-11 17:18 ` [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks Dave Hansen
2018-12-11 17:52 ` Tim Chen
2018-12-11 17:53 ` Andi Kleen
2018-12-11 23:46 ` Li, Aubrey
2018-12-12 0:14 ` Arjan van de Ven
2018-12-12 0:59 ` Li, Aubrey
2018-12-12 1:06 ` Dave Hansen
2018-12-11 17:20 ` Dave Hansen
2018-12-12 0:34 ` Li, Aubrey
2018-12-12 0:39 ` Dave Hansen
2018-12-12 16:55 ` David Laight
2018-12-12 18:00 ` Andi Kleen [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181212180046.GG25620@tassilo.jf.intel.com \
--to=ak@linux.intel.com \
--cc=David.Laight@aculab.com \
--cc=arjan@linux.intel.com \
--cc=aubrey.li@intel.com \
--cc=aubrey.li@linux.intel.com \
--cc=dave.hansen@intel.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=tim.c.chen@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.