From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Jes Sorensen <jes@sgi.com>
Cc: "Zhang, Xiantao" <xiantao.zhang@intel.com>,
Carsten Otte <cotte@de.ibm.com>,
"Luck, Tony" <tony.luck@intel.com>,
linux-ia64@vger.kernel.org, kvm-ia64-devel@lists.sourceforge.net,
kvm-devel@lists.sourceforge.net,
virtualization@lists.linux-foundation.org, "Xu,
Anthony" <anthony.xu@intel.com>
Subject: Re: [02/17][PATCH] Implement smp_call_function_mask for ia64 - V8
Date: Mon, 31 Mar 2008 15:02:22 +0000 [thread overview]
Message-ID: <47F0FCFE.5010106@goop.org> (raw)
In-Reply-To: <47F0AB18.2010707@sgi.com>
Jes Sorensen wrote:
> I'm a little wary of the performance impact of this change. Doing a
> cpumask compare on all smp_call_function calls seems a little expensive.
> Maybe it's just noise in the big picture compared to the actual cost of
> the IPIs, but I thought I'd bring it up.
>
> Keep in mind that a cpumask can be fairly big these days, max NR_CPUS
> is currently 4096. For those booting a kernel with NR_CPUS at 4096 on
> a dual CPU machine, it would be a bit expensive.
>
Unless your hardware has remarkably fast IPIs, I think really the cost
of scanning 512 bytes is going to be in the noise...
This change has been on the x86 side for ages, and not even Ingo made a
peep about it ;)
> Why not keep smp_call_function() the way it was before, rather than
> implementing it via the call to smp_call_function_mask()?
>
Because Xen needs a different core implementation (because of its
different IPI implementation), and it would be better to just have to do
one of them rather than N.
J
WARNING: multiple messages have this Message-ID (diff)
From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Jes Sorensen <jes@sgi.com>
Cc: "Zhang, Xiantao" <xiantao.zhang@intel.com>,
Carsten Otte <cotte@de.ibm.com>,
"Luck, Tony" <tony.luck@intel.com>,
linux-ia64@vger.kernel.org, kvm-ia64-devel@lists.sourceforge.net,
kvm-devel@lists.sourceforge.net,
virtualization@lists.linux-foundation.org, "Xu,
Anthony" <anthony.xu@intel.com>
Subject: Re: [02/17][PATCH] Implement smp_call_function_mask for ia64 - V8
Date: Mon, 31 Mar 2008 08:02:22 -0700 [thread overview]
Message-ID: <47F0FCFE.5010106@goop.org> (raw)
In-Reply-To: <47F0AB18.2010707@sgi.com>
Jes Sorensen wrote:
> I'm a little wary of the performance impact of this change. Doing a
> cpumask compare on all smp_call_function calls seems a little expensive.
> Maybe it's just noise in the big picture compared to the actual cost of
> the IPIs, but I thought I'd bring it up.
>
> Keep in mind that a cpumask can be fairly big these days, max NR_CPUS
> is currently 4096. For those booting a kernel with NR_CPUS at 4096 on
> a dual CPU machine, it would be a bit expensive.
>
Unless your hardware has remarkably fast IPIs, I think really the cost
of scanning 512 bytes is going to be in the noise...
This change has been on the x86 side for ages, and not even Ingo made a
peep about it ;)
> Why not keep smp_call_function() the way it was before, rather than
> implementing it via the call to smp_call_function_mask()?
>
Because Xen needs a different core implementation (because of its
different IPI implementation), and it would be better to just have to do
one of them rather than N.
J
next prev parent reply other threads:[~2008-03-31 15:02 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-28 9:59 [02/17][PATCH] Implement smp_call_function_mask for ia64 Zhang, Xiantao
2008-03-30 11:42 ` [kvm-ia64-devel] " Avi Kivity
2008-03-30 11:42 ` [kvm-ia64-devel] [02/17][PATCH] Implement smp_call_function_mask Avi Kivity
2008-03-30 11:42 ` [kvm-ia64-devel] [02/17][PATCH] Implement smp_call_function_mask for ia64 Avi Kivity
2008-03-31 1:40 ` Zhang, Xiantao
2008-03-31 1:40 ` Zhang, Xiantao
2008-03-31 8:25 ` [02/17][PATCH] Implement smp_call_function_mask for ia64 - V8 Zhang, Xiantao
2008-03-31 9:12 ` Jes Sorensen
2008-03-31 9:12 ` Jes Sorensen
2008-03-31 9:12 ` Jes Sorensen
2008-03-31 10:17 ` [kvm-devel] [02/17][PATCH] Implement smp_call_function_mask foria64 " Zhang, Xiantao
2008-03-31 10:17 ` Zhang, Xiantao
2008-03-31 15:02 ` Jeremy Fitzhardinge [this message]
2008-03-31 15:02 ` [02/17][PATCH] Implement smp_call_function_mask for ia64 " Jeremy Fitzhardinge
2008-04-01 8:34 ` Jes Sorensen
2008-04-01 8:34 ` Jes Sorensen
2008-04-01 8:34 ` Jes Sorensen
2008-04-01 16:06 ` Jeremy Fitzhardinge
2008-04-01 16:06 ` Jeremy Fitzhardinge
2008-04-01 16:06 ` Jeremy Fitzhardinge
2008-04-02 7:30 ` Jes Sorensen
2008-04-02 7:30 ` Jes Sorensen
2008-04-02 23:48 ` Luck, Tony
2008-04-02 23:48 ` Luck, Tony
2008-04-02 23:48 ` Luck, Tony
2008-04-02 7:30 ` Jes Sorensen
2008-03-31 15:02 ` Jeremy Fitzhardinge
-- strict thread matches above, loose matches on Subject: below --
2008-03-31 8:25 Zhang, Xiantao
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