LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Suresh Siddha <suresh.b.siddha@intel.com>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>,
	mingo@elte.hu, hpa@zytor.com, tglx@linutronix.de,
	andi@firstfloor.org, hch@infradead.org,
	linux-kernel@vger.kernel.org,
	Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [patch 1/2] x86, fpu: split FPU state from task struct - v5
Date: Tue, 11 Mar 2008 13:19:22 -0700	[thread overview]
Message-ID: <20080311201921.GE15909@linux-os.sc.intel.com> (raw)
In-Reply-To: <20080311050644.GB4589@martell.zuzino.mipt.ru>

On Tue, Mar 11, 2008 at 08:07:34AM +0300, Alexey Dobriyan wrote:
> On Mon, Mar 10, 2008 at 03:28:04PM -0700, Suresh Siddha wrote:
> > Split the FPU save area from the task struct. This allows easy migration
> > of FPU context, and it's generally cleaner. It also allows the following
> > two optimizations:
> > 
> > 1) only allocate when the application actually uses FPU, so in the first
> > lazy FPU trap. This could save memory for non-fpu using apps. Next patch
> > does this lazy allocation.
> > 
> > 2) allocate the right size for the actual cpu rather than 512 bytes always.
> > Patches enabling xsave/xrstor support (coming shortly) will take advantage
> > of this.
> 
> Ugh, not seeing patch, but judging from description it will make
> "choose wrong CONFIG_M* and fxsave will corrupt random FPU state" situation
> likely?

No. CONFIG_M* doesn't determine the size of the state. Feature information from
the 'cpuid' instruction will dictate the size allocated/used. Anyhow, please
wait for the xsave patches.

> 
> > --- linux-2.6-x86.orig/arch/x86/kernel/process_64.c
> > +++ linux-2.6-x86/arch/x86/kernel/process_64.c
> > @@ -634,7 +634,7 @@
> >  
> >  	/* we're going to use this soon, after a few expensive things */
> >  	if (next_p->fpu_counter>5)
> > -		prefetch(&next->i387.fxsave);
> > +		prefetch(next->xstate);
> 
> Can we please give it better name, like fpu_state? It's a member of
> task_struct after all.

It need not be only FPU. We can have non-math state here aswell.

selected 'xstate' for extended state. I am all open for any reasonable name,
reflecting math, extended math(fsave/fxsave/..) and future math/
non-math extensions.

> >  {
> >  	unsigned long oldcr0 = read_cr0();
> > -	extern void __bad_fxsave_alignment(void);
> > -
> > -	if (offsetof(struct task_struct, thread.i387.fxsave) & 15)
> > -		__bad_fxsave_alignment();
> 
> I think removal of such checks needs giving necessary alignment to cache.
> Previously it worked because of __aligned((16)) and L1_CACHE_SHIFT
> combo.

alignment is now specified as part of kmem_cache_create() and checed
in the allocation routines.

thanks,
suresh

      parent reply	other threads:[~2008-03-11 20:21 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-10 22:28 Suresh Siddha
2008-03-10 22:28 ` [patch 2/2] x86, fpu: lazy allocation of FPU area " Suresh Siddha
2008-03-11  9:08   ` Ingo Molnar
2008-03-11 20:57     ` Suresh Siddha
2008-03-10 22:56 ` [patch 1/2] x86, fpu: split FPU state from task struct " Andi Kleen
2008-03-11  5:07 ` Alexey Dobriyan
2008-03-11  8:35   ` Ingo Molnar
2008-03-11 10:09     ` Alexey Dobriyan
2008-03-11 10:11       ` Ingo Molnar
2008-03-11 20:22         ` Suresh Siddha
2008-03-11 20:19   ` Suresh Siddha [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=20080311201921.GE15909@linux-os.sc.intel.com \
    --to=suresh.b.siddha@intel.com \
    --cc=adobriyan@gmail.com \
    --cc=andi@firstfloor.org \
    --cc=arjan@linux.intel.com \
    --cc=hch@infradead.org \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@elte.hu \
    --cc=tglx@linutronix.de \
    --subject='Re: [patch 1/2] x86, fpu: split FPU state from task struct - v5' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).