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From: Thomas Gleixner <tglx@linutronix.de>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	linux-mips@linux-mips.org, linux-mm@kvack.org,
	WireGuard mailing list <wireguard@lists.zx2c4.com>,
	k@vodka.home.kg
Subject: Re: Proposal: HAVE_SEPARATE_IRQ_STACK?
Date: Thu, 10 Nov 2016 14:00:33 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1611101351260.3501@nanos> (raw)
In-Reply-To: <CAHmME9pHYA82M3iDNfDtDE96gFaZORSsEAn_KnePd3rhFioqHQ@mail.gmail.com>

On Thu, 10 Nov 2016, Jason A. Donenfeld wrote:
> On Thu, Nov 10, 2016 at 10:03 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > Does the slowdown come from the kmalloc overhead or mostly from the less
> > efficient code?
> >
> > If it's mainly kmalloc, then you can preallocate the buffer once for the
> > kthread you're running in and be done with it. If it's the code, then bad
> > luck.
> 
> I fear both. GCC can optimize stack variables in ways that it cannot
> optimize various memory reads and writes.

The question is how much of it is code and how much of it is the kmalloc.
 
> Strangely, the solution that appeals to me most at the moment is to
> kmalloc (or vmalloc?) a new stack, copy over thread_info, and fiddle
> with the stack registers. I don't see any APIs, however, for a
> platform independent way of doing this. And maybe this is a horrible
> idea. But at least it'd allow me to keep my stack-based code the
> same...

Do not even think about going there. That's going to be a major
mess.

As a short time workaround you can increase THREAD_SIZE_ORDER for now and
then fix it proper with switching to seperate irq stacks.

Thanks,

	tglx

  reply	other threads:[~2016-11-10 13:03 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-09 21:27 Proposal: HAVE_SEPARATE_IRQ_STACK? Jason A. Donenfeld
2016-11-09 21:40 ` Thomas Gleixner
2016-11-09 23:34   ` Jason A. Donenfeld
2016-11-10  9:03     ` Thomas Gleixner
2016-11-10 11:41       ` Jason A. Donenfeld
2016-11-10 13:00         ` Thomas Gleixner [this message]
2016-11-10 17:39           ` Jason A. Donenfeld
2016-11-10 16:36         ` Matt Redfearn
2016-11-10 17:37           ` Jason A. Donenfeld
2016-11-10  0:17 ` David Daney
2016-11-10  1:47   ` Jason A. Donenfeld

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