From: Rik van Riel <riel@surriel.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
"Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Andrew Lutomirski <luto@kernel.org>,
dave.hansen@linux.intel.com, LKML <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>
Subject: Re: Lazy FPU restoration / moving kernel_fpu_end() to context switch
Date: Wed, 11 Jul 2018 16:10:33 -0400 [thread overview]
Message-ID: <1531339833.26425.1.camel@surriel.com> (raw)
In-Reply-To: <20180711162850.52jmzsuwegpk7rag@breakpoint.cc>
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On Wed, 2018-07-11 at 18:28 +0200, Sebastian Andrzej Siewior wrote:
> On 2018-06-15 22:33:47 [+0200], Jason A. Donenfeld wrote:
> > On Fri, Jun 15, 2018 at 8:32 PM Andy Lutomirski <luto@kernel.org>
> > wrote:
> > > quite in the form you imagined. The idea that we've tossed
> > > around is
> > > to restore FPU state on return to user mode. Roughly, we'd
> > > introduce
> > > a new thread flag TIF_FPU_UNLOADED (name TBD).
> > > prepare_exit_to_usermode() would notice this flag, copy the
> > > fpstate to
> > > fpregs, and clear the flag. (Or maybe exit_to_usermode_loop() --
> > > No
> > > one has quite thought it through, but I think it should be
> > > outside the
> > > loop.) We'd update all the FPU accessors to understand the flag.
> >
> > Yes! This is exactly what I was thinking. Then those calls to
> > begin()
> > and end() could be placed as close to the actual FPU usage as
> > possible.
>
> I was thinking about this myself. Did anyone try to hack something in
> the meantime? I might want to look into this, too :)
I have implemented this before, back before the
big rewrite of the syscall entry and exit code.
It seemed to work fine.
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prev parent reply other threads:[~2018-07-11 20:10 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-15 13:11 Lazy FPU restoration / moving kernel_fpu_end() to context switch Jason A. Donenfeld
2018-06-15 16:25 ` Thomas Gleixner
2018-06-15 18:33 ` Brian Gerst
2018-06-15 19:34 ` Peter Zijlstra
2018-06-15 20:30 ` Jason A. Donenfeld
2018-06-18 9:44 ` Peter Zijlstra
2018-06-18 15:25 ` Jason A. Donenfeld
2018-06-15 18:31 ` Andy Lutomirski
2018-06-15 18:40 ` Rik van Riel
2018-06-15 18:41 ` Dave Hansen
2018-06-15 18:49 ` Andy Lutomirski
2018-06-15 18:48 ` Dave Hansen
2018-06-15 18:53 ` Andy Lutomirski
2018-06-15 20:27 ` Jason A. Donenfeld
2018-06-15 20:48 ` Jason A. Donenfeld
2018-06-19 11:43 ` David Laight
2018-06-19 13:08 ` Thomas Gleixner
2018-06-15 20:33 ` Jason A. Donenfeld
2018-06-15 20:42 ` Dave Hansen
2018-06-15 20:52 ` Andy Lutomirski
2018-06-15 20:56 ` Rik van Riel
2018-07-11 16:28 ` Sebastian Andrzej Siewior
2018-07-11 20:10 ` Rik van Riel [this message]
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