linux-kernel - Re: Lazy FPU restoration / moving kernel_fpu

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Message-ID: <20180618094447.GG2458@hirez.programming.kicks-ass.net>
Date:   Mon, 18 Jun 2018 11:44:47 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Andy Lutomirski <luto@...capital.net>
Subject: Re: Lazy FPU restoration / moving kernel_fpu_end() to context switch

On Fri, Jun 15, 2018 at 10:30:46PM +0200, Jason A. Donenfeld wrote:
> On Fri, Jun 15, 2018 at 9:34 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > Didn't we recently do a bunch of crypto patches to help with this?
> >
> > I think they had the pattern:
> >
> >         kernel_fpu_begin();
> >         for (units-of-work) {
> >                 do_unit_of_work();
> >                 if (need_resched()) {
> >                         kernel_fpu_end();
> >                         cond_resched();
> >                         kernel_fpu_begin();
> >                 }
> >         }
> >         kernel_fpu_end();
> 
> Right, so that's the thing -- this is an optimization easily available
> to individual crypto primitives. But I'm interested in applying this
> kind of optimization to an entire queue of, say, tiny packets, where
> each packet is processed individually. Or, to a cryptographic
> construction, where several different primitives are used, such that
> it'd be meaningful not to have to get the performance hit of
> end()begin() in between each and everyone of them.

I'm confused.. how does the above not apply to your situation?