From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Giuliano Pochini <pochini@shiny.it>
Cc: linuxppc-dev list <linuxppc-dev@lists.linuxppc.org>,
Lee Braiden <lee_b@member.fsf.org>
Subject: Re: SMP kernels on single processor machines
Date: Fri, 21 May 2004 21:11:06 +1000 [thread overview]
Message-ID: <1085137865.6133.2.camel@gaston> (raw)
In-Reply-To: <XFMail.20040521123444.pochini@shiny.it>
On Fri, 2004-05-21 at 20:34, Giuliano Pochini wrote:
>
> 2.6.6 has the CONFIG_PREEMPT option so I thought it was stable.
> Isn't it ? What are the known problem ? Is only preempt+smp
> known to have problems ?
Well, there are 3 different things.
One is stability. I don't know of any ppc-specific problem with preempt,
though I do have reports of people experiencing problems (mostly various
kinds of segfaults) when it's enabled. I'm not sure what is to blame at
this point, possibly one of the filesystems.
Another is overhead. Preempt definitely adds overhead to the kernel. The
spinlocks, on an UP kernel, are mostly NOPs, while with preempt, they are
actually implemented (among others). Overall, preempt adds overhead to the
kernel.
Finally, the supposed benefit. Mostly a myth imho.
For those who didn't get it (yes, that happens), the kernel, even without
preempt, will preempt user processes :) Linux has always been a preemptible
operating system. CONFIG_PREEMPT only concerns the ability for the kernel
to preempt itself when a process triggers a potentially long operations
within the kernel.
Ben.
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2004-05-21 11:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-05-20 10:58 SMP kernels on single processor machines Jens Schmalzing
2004-05-20 11:48 ` Lee Braiden
2004-05-20 23:56 ` Benjamin Herrenschmidt
2004-05-21 10:34 ` Giuliano Pochini
2004-05-21 11:11 ` Benjamin Herrenschmidt [this message]
2004-05-21 12:30 ` Lee Braiden
2004-05-21 12:58 ` Marius Groeger
2004-05-21 23:11 ` Benjamin Herrenschmidt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1085137865.6133.2.camel@gaston \
--to=benh@kernel.crashing.org \
--cc=lee_b@member.fsf.org \
--cc=linuxppc-dev@lists.linuxppc.org \
--cc=pochini@shiny.it \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).