From: Robin Holt <holt@sgi.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <npiggin@suse.de>, Robin Holt <holt@sgi.com>,
"Luck, Tony" <tony.luck@intel.com>,
Dimitri Sivanich <sivanich@sgi.com>,
"linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
Greg KH <greg@kroah.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Gregory Haskins <ghaskins@novell.com>,
Tony Luck <tony.luck@gmail.com>
Subject: Re: [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems
Date: Wed, 07 Jan 2009 09:43:28 +0000 [thread overview]
Message-ID: <20090107094328.GD3850@sgi.com> (raw)
In-Reply-To: <1231313289.11687.172.camel@twins>
On Wed, Jan 07, 2009 at 08:28:09AM +0100, Peter Zijlstra wrote:
> That's basically what the HAVE_UNSTABLE_SCHED_CLOCK code does. It takes
> a tick timestamp and tries to improve on that by using strict per cpu
> sched_clock() deltas.
>
> What we do to obtain remote time, is basically calculate local time and
> pull remote time fwd if that was behind.
But what happens when the remote clock then takes a single tick and
pulls forward a different remote clock by both your tick and its tick.
Multiply that by 4096 and I am starting to feel that time is likely to
go racing forward in a really random fashion.
> While doing that, it filters out any backward motion and large fwd leaps
> so as to stay no worse than a jiffie clock.
WARNING: multiple messages have this Message-ID (diff)
From: Robin Holt <holt@sgi.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <npiggin@suse.de>, Robin Holt <holt@sgi.com>,
"Luck, Tony" <tony.luck@intel.com>,
Dimitri Sivanich <sivanich@sgi.com>,
"linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
Greg KH <greg@kroah.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Gregory Haskins <ghaskins@novell.com>,
Tony Luck <tony.luck@gmail.com>
Subject: Re: [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems
Date: Wed, 7 Jan 2009 03:43:28 -0600 [thread overview]
Message-ID: <20090107094328.GD3850@sgi.com> (raw)
In-Reply-To: <1231313289.11687.172.camel@twins>
On Wed, Jan 07, 2009 at 08:28:09AM +0100, Peter Zijlstra wrote:
> That's basically what the HAVE_UNSTABLE_SCHED_CLOCK code does. It takes
> a tick timestamp and tries to improve on that by using strict per cpu
> sched_clock() deltas.
>
> What we do to obtain remote time, is basically calculate local time and
> pull remote time fwd if that was behind.
But what happens when the remote clock then takes a single tick and
pulls forward a different remote clock by both your tick and its tick.
Multiply that by 4096 and I am starting to feel that time is likely to
go racing forward in a really random fashion.
> While doing that, it filters out any backward motion and large fwd leaps
> so as to stay no worse than a jiffie clock.
next prev parent reply other threads:[~2009-01-07 9:43 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-06 16:27 [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems Dimitri Sivanich
2009-01-06 16:27 ` Dimitri Sivanich
2009-01-06 17:12 ` Greg KH
2009-01-06 17:12 ` Greg KH
2009-01-06 20:15 ` Luck, Tony
2009-01-06 20:15 ` Luck, Tony
2009-01-06 20:19 ` Robin Holt
2009-01-06 20:19 ` Robin Holt
2009-01-06 20:34 ` Luck, Tony
2009-01-06 20:34 ` Luck, Tony
2009-01-06 20:57 ` Peter Zijlstra
2009-01-06 20:57 ` Peter Zijlstra
2009-01-06 22:50 ` Robin Holt
2009-01-06 22:50 ` Robin Holt
2009-01-06 23:16 ` Peter Zijlstra
2009-01-06 23:16 ` Peter Zijlstra
2009-01-07 3:00 ` Nick Piggin
2009-01-07 3:00 ` Nick Piggin
2009-01-07 3:16 ` Jack Steiner
2009-01-07 3:16 ` Jack Steiner
2009-01-07 7:28 ` Peter Zijlstra
2009-01-07 7:28 ` Peter Zijlstra
2009-01-07 7:40 ` Nick Piggin
2009-01-07 7:40 ` Nick Piggin
2009-01-07 9:43 ` Robin Holt [this message]
2009-01-07 9:43 ` Robin Holt
2009-01-07 9:53 ` Peter Zijlstra
2009-01-07 9:53 ` Peter Zijlstra
2009-01-07 13:32 ` Dimitri Sivanich
2009-01-07 13:32 ` Dimitri Sivanich
2009-01-07 15:16 ` Peter Zijlstra
2009-01-07 15:16 ` Peter Zijlstra
2009-01-15 18:48 ` Greg KH
2009-01-15 18:48 ` Greg KH
2009-01-15 19:21 ` Luck, Tony
2009-01-15 19:21 ` Luck, Tony
2009-01-22 19:04 ` Greg KH
2009-01-22 19:04 ` Greg KH
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