| From: |
| David Chinner <dgc@sgi.com> |
| To: |
| Eric Sandeen <sandeen@sandeen.net> |
| Subject: |
| Re: x86: 4kstacks default |
| Date: |
| Mon, 21 Apr 2008 08:53:11 +1000 |
| Message-ID: |
| <20080420225311.GI108924158@sgi.com> |
| Cc: |
| Arjan van de Ven <arjan@infradead.org>,
Shawn Bohrer <shawn.bohrer@gmail.com>,
Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de> |
| Archive‑link: | |
Article |
On Sat, Apr 19, 2008 at 09:36:16PM -0500, Eric Sandeen wrote:
> Arjan van de Ven wrote:
>
> > On the flipside the arguments tend to be
> > 1) certain stackings of components still runs the risk of overflowing
> > 2) I want to run ndiswrapper
> > 3) general, unspecified uneasyness.
> >
> > For 1), we need to know which they are, and then solve them, because even on x86-64 with 8k stacks
> > they can be a problem (just because the stack frames are bigger, although not quite double, there).
>
> Except, apparently, not, at least in my experience.
>
> Ask the xfs guys if they see stack overflows on x86_64, or on x86.
We see them regularly enough on x86 to know that the first question
to any strange crash is "are you using 4k stacks?". In comparison,
I have never heard of a single stack overflow on x86_64....
> I've personally never seen common stack problems with xfs on x86_64, but
> it's very common on x86. I don't have a great answer for why, but
> that's my anecdotal evidence.
Why? Because XFS makes extensive use of 64 bit types and so stack
usage in the critical paths changes by a relatively small amount
between 32 bit and 64 bit machines. IIRC, x86_64 only uses about
30% more stack than x86. So given that the stack doubles on x86_64
and we only increase usage (in XFS) from about 1500 bytes to 2000
bytes of stack usage, we have *lots* more stack space to spare on
x86_64 compared to 4k stacks on x86....
Cheers,
Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group
