Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 18 Jun 2018 11:44:47 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>
Subject: Re: Lazy FPU restoration / moving kernel_fpu_end() to context switch
Message-ID: <20180618094447.GG2458@hirez.programming.kicks-ass.net>
References: <CAHmME9pBqGhCjdwx64GxYTKWiMkDNY3v2gnVL_Xm2q=3guOAsQ@mail.gmail.com>
 <alpine.DEB.2.21.1806151815080.1582@nanos.tec.linutronix.de>
 <20180615193438.GE2458@hirez.programming.kicks-ass.net>
 <CAHmME9qr4PzsGKK2r2sGoCty_Yum_3UqUdL76CPOAOq18K+a4A@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHmME9qr4PzsGKK2r2sGoCty_Yum_3UqUdL76CPOAOq18K+a4A@mail.gmail.com>
User-Agent: Mutt/1.10.0 (2018-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@infradead.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?