From: Michael Ellerman <michael@ellerman.id.au>
To: Brian King <brking@linux.vnet.ibm.com>
Cc: linuxppc-dev@ozlabs.org
Subject: Re: Badness in xics_ipi_dispatch
Date: Wed, 21 Apr 2010 11:43:54 +1000 [thread overview]
Message-ID: <1271814234.13262.36.camel@concordia> (raw)
In-Reply-To: <4BCE27E8.4090101@linux.vnet.ibm.com>
[-- Attachment #1: Type: text/plain, Size: 1156 bytes --]
On Tue, 2010-04-20 at 17:17 -0500, Brian King wrote:
> In stress testing enabling and disabling of SMT, we are regularly
> seeing the badness warning below. Looking through the cpu offline
> path, this is what I see:
>
> 1. stop_cpu: IRQ's get disabled
> 2. pseries_cpu_disable: set cpu offline (no barriers after this)
> 3. xics_migrate_irqs_away: Remove ourselves from the GIQ, but still allow
> IPIs
> 4. stop_cpu: IRQ's get enabled again (local_irq_enable)
>
> It looks to me like there is plenty of opportunity between 1 and 2 for
> an IPI to get queued, resulting in the badness below. Is there something
> in xics_migrate_irqs_away that should clear any pending IPIs? If there
> is, maybe the solution is as simple as adding a barrier after marking
> the cpu offline. Or is the warning bogus and we should just remove it?
It looks like xics_migrate_irqs_away() doesn't do anything about IPIs,
at least the comment says "Allow IPIs again". So I don't see what's to
stop you just taking another IPI after you reenable interrupts in
stop_cpu(). Maybe xics_ipi_dispatch() should just return if the cpu is
offline?
cheers
[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 197 bytes --]
next prev parent reply other threads:[~2010-04-21 1:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-20 22:17 Badness in xics_ipi_dispatch Brian King
2010-04-21 1:43 ` Michael Ellerman [this message]
2010-07-20 5:35 ` Darren Hart
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=1271814234.13262.36.camel@concordia \
--to=michael@ellerman.id.au \
--cc=brking@linux.vnet.ibm.com \
--cc=linuxppc-dev@ozlabs.org \
/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).