Date: Mon, 11 Aug 2008 13:19:01 -0700
From: Suresh Siddha <suresh.b.siddha@intel.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>,
       "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
       Herbert Xu <herbert@gondor.apana.org.au>,
       Wolfgang Walter <wolfgang.walter@stwm.de>,
       "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "viro@ZenIV.linux.org.uk" <viro@zeniv.linux.org.uk>,
       "vegard.nossum@gmail.com" <vegard.nossum@gmail.com>,
       Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Kernel oops with 2.6.26, padlock and ipsec: probably problem with fpu state changes
Message-ID: <20080811201901.GN13158@linux-os.sc.intel.com>
References: <20080808231121.GA13158@linux-os.sc.intel.com> <20080809143727.GA30499@gondor.apana.org.au> <200808091757.32999.wolfgang.walter@stwm.de> <489DC15D.9070308@zytor.com> <20080809185224.GH13158@linux-os.sc.intel.com> <20080809193724.GJ13158@linux-os.sc.intel.com> <20080810030521.GA2332@gondor.apana.org.au> <20080811190131.GL13158@linux-os.sc.intel.com> <20080811192203.GC12788@elte.hu> <48A0920B.30306@zytor.com>
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On Mon, Aug 11, 2008 at 12:24:59PM -0700, H. Peter Anvin wrote:
> Ingo Molnar wrote:
> > * Suresh Siddha <suresh.b.siddha@intel.com> wrote:
> >
> >> Reported-and-bisected-by: Wolfgang Walter <wolfgang.walter@stwm.de>
> >> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
> >
> > no fundamental objection to the x86 bits.
> >
> > shouldnt this:
> >
> > +       if (!in_interrupt())
> > +               return 0;
> >
> > just be eliminated and the cr0/TS save/restore be made unconditional?
> > irq-assymetric APIs are not nice in general.
> >
> > Reading/setting cr0 isnt _that_ slow. (or if it is, by how much does it
> > slow things down, exactly?)
> >
> 
> Setting it is relatively slow.  I think that's part of the reason for
> special instructions to muck with the TS flag.
> 
> Reading it might be slow on obsolete processors.

In addition to the slowness(Wolf has collected some data with earlier
patch and I think it showed a double digit increase in cpu utilization with
some crypt tests):

we can't unconditionally do clts() in the process context. We have
to disable pre-emption to avoid interactions with context switch and
lazy restore. So there will be RT latency issues aswell.

thanks,
suresh
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