From: Ingo Molnar <mingo@kernel.org>
To: Alexander Gordeev <agordeev@redhat.com>
Cc: Arjan van de Ven <arjan@infradead.org>,
linux-kernel@vger.kernel.org, x86@kernel.org,
Suresh Siddha <suresh.b.siddha@intel.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Yinghai Lu <yinghai@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 2/3] x86: x2apic/cluster: Make use of lowest priority delivery mode
Date: Mon, 21 May 2012 16:59:04 +0200 [thread overview]
Message-ID: <20120521145904.GA7068@gmail.com> (raw)
In-Reply-To: <20120521144812.GD28930@dhcp-26-207.brq.redhat.com>
* Alexander Gordeev <agordeev@redhat.com> wrote:
> > So I think we need to tread carefully here.
>
> Kernel parameter? IRQ line flag? Totally opposed? :)
Undecided and sceptical, because: -ENONUMBERS :-)
The kernel actually tries to have as much locality as we can
hide from the user.
For example we don't execute tasks for 100 usecs on one CPU,
then jump to another CPU and execute 100 usecs there, then to
yet another CPU to create an 'absolutely balanced use of CPU
resources'. Why? Because the cache-misses would be killing us.
When a device is generating ten thousand irqs a second then
round-robining the IRQs is equivalent to switching a CPU every
100 usecs.
There's another cost: tasks tend to try to migrate to sources of
wakeups. So if an IRQ wakes up a task then we will try to
execute the task locally, to have locality of access between the
data that the IRQ handler has touched, and the task that makes
use of it. Round-robining the IRQ in that situations means that
the task either follows the IRQ and round-robins (bad), or that
it stays remote to the IRQ data (not good either).
So, I'm sceptical :-/
Your other two patches looked sensible - will they apply fine
after each other, without the round-robin patch which is still
under discussion, or is there a dependency?
Thanks,
Ingo
next prev parent reply other threads:[~2012-05-21 14:59 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-18 10:26 [PATCH 2/3] x86: x2apic/cluster: Make use of lowest priority delivery mode Alexander Gordeev
2012-05-18 14:41 ` Cyrill Gorcunov
2012-05-18 15:42 ` Alexander Gordeev
2012-05-18 15:51 ` Cyrill Gorcunov
2012-05-19 10:47 ` Cyrill Gorcunov
2012-05-21 7:11 ` Alexander Gordeev
2012-05-21 9:46 ` Cyrill Gorcunov
2012-05-19 20:53 ` Yinghai Lu
2012-05-21 8:13 ` Alexander Gordeev
2012-05-21 23:02 ` Yinghai Lu
2012-05-21 23:33 ` Yinghai Lu
2012-05-22 9:36 ` Alexander Gordeev
2012-05-21 23:44 ` Suresh Siddha
2012-05-21 23:58 ` [PATCH 1/2] x86, irq: update irq_cfg domain unless the new affinity is a subset of the current domain Suresh Siddha
2012-05-21 23:58 ` [PATCH 2/2] x2apic, cluster: use all the members of one cluster specified in the smp_affinity mask for the interrupt desintation Suresh Siddha
2012-05-22 7:04 ` Ingo Molnar
2012-05-22 7:34 ` Cyrill Gorcunov
2012-05-22 17:21 ` Suresh Siddha
2012-05-22 17:39 ` Cyrill Gorcunov
2012-05-22 17:42 ` Suresh Siddha
2012-05-22 17:45 ` Cyrill Gorcunov
2012-05-22 20:03 ` Yinghai Lu
2012-06-06 15:04 ` [tip:x86/apic] x86/x2apic/cluster: Use all the members of one cluster specified in the smp_affinity mask for the interrupt destination tip-bot for Suresh Siddha
2012-06-06 22:21 ` Yinghai Lu
2012-06-06 23:14 ` Suresh Siddha
2012-06-06 15:03 ` [tip:x86/apic] x86/irq: Update irq_cfg domain unless the new affinity is a subset of the current domain tip-bot for Suresh Siddha
2012-08-07 15:31 ` Robert Richter
2012-08-07 15:41 ` do_IRQ: 1.55 No irq handler for vector (irq -1) Borislav Petkov
2012-08-07 16:24 ` Suresh Siddha
2012-08-07 17:28 ` Robert Richter
2012-08-07 17:47 ` Suresh Siddha
2012-08-07 17:45 ` Eric W. Biederman
2012-08-07 20:57 ` Borislav Petkov
2012-08-07 22:39 ` Suresh Siddha
2012-08-08 8:58 ` Robert Richter
2012-08-08 11:04 ` Borislav Petkov
2012-08-08 19:16 ` Suresh Siddha
2012-08-14 17:02 ` [tip:x86/urgent] x86, apic: fix broken legacy interrupts in the logical apic mode tip-bot for Suresh Siddha
2012-06-06 17:20 ` [PATCH 1/2] x86, irq: update irq_cfg domain unless the new affinity is a subset of the current domain Alexander Gordeev
2012-06-06 23:02 ` Suresh Siddha
2012-06-16 0:25 ` Suresh Siddha
2012-06-18 9:17 ` Alexander Gordeev
2012-06-19 0:51 ` Suresh Siddha
2012-06-19 23:43 ` [PATCH 1/2] x86, apic: optimize cpu traversal in __assign_irq_vector() using domain membership Suresh Siddha
2012-06-19 23:43 ` [PATCH 2/2] x86, x2apic: limit the vector reservation to the user specified mask Suresh Siddha
2012-06-20 5:56 ` Yinghai Lu
2012-06-21 9:04 ` Alexander Gordeev
2012-06-21 21:51 ` Suresh Siddha
2012-06-20 5:53 ` [PATCH 1/2] x86, apic: optimize cpu traversal in __assign_irq_vector() using domain membership Yinghai Lu
2012-06-21 8:31 ` Alexander Gordeev
2012-06-21 21:53 ` Suresh Siddha
2012-06-20 0:18 ` [PATCH 1/2] x86, irq: update irq_cfg domain unless the new affinity is a subset of the current domain Suresh Siddha
2012-06-21 11:00 ` Alexander Gordeev
2012-06-21 21:58 ` Suresh Siddha
2012-05-22 10:12 ` [PATCH 2/3] x86: x2apic/cluster: Make use of lowest priority delivery mode Alexander Gordeev
2012-05-21 8:22 ` Ingo Molnar
2012-05-21 9:36 ` Alexander Gordeev
2012-05-21 12:40 ` Ingo Molnar
2012-05-21 14:48 ` Alexander Gordeev
2012-05-21 14:59 ` Ingo Molnar [this message]
2012-05-21 15:22 ` Alexander Gordeev
2012-05-21 15:34 ` Cyrill Gorcunov
2012-05-21 15:36 ` Linus Torvalds
2012-05-21 18:07 ` Suresh Siddha
2012-05-21 18:18 ` Linus Torvalds
2012-05-21 18:37 ` Suresh Siddha
2012-05-21 19:30 ` Ingo Molnar
2012-05-21 19:15 ` Ingo Molnar
2012-05-21 19:56 ` Suresh Siddha
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