From: Andrew Morton <akpm@linux-foundation.org>
To: Jonathan Corbet <corbet@lwn.net>
Cc: linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
Roman Zippel <zippel@linux-m68k.org>
Subject: Re: [PATCH] msleep() with hrtimers
Date: Tue, 7 Aug 2007 12:40:09 -0700 [thread overview]
Message-ID: <20070807124009.9f6c2247.akpm@linux-foundation.org> (raw)
In-Reply-To: <15327.1186166232@lwn.net>
On Fri, 03 Aug 2007 12:37:12 -0600
Jonathan Corbet <corbet@lwn.net> wrote:
>
> Here's the second (and probably final) posting of the msleep() with
> hrtimers patch. The problem being addressed here is that the current
> msleep() will stop for a minimum of two jiffies, meaning that, on a
> HZ=100 system, msleep(1) delays for for about 20ms. In a driver with
> one such delay for each of 150 or so register setting operations, the
> extra time adds up to a few seconds.
>
> This patch addresses the situation by using hrtimers. On tickless
> systems with working timers, msleep(1) now sleeps for 1ms, even with
> HZ=100.
>
> Most comments last time were favorable. The one dissenter was Roman,
> who worries about the overhead of using hrtimers for this operation; my
> understanding is that he would rather see a really_msleep() function for
> those who actually want millisecond resolution. I'm not sure how to
> characterize what the cost could be, but it can only be buried by the
> fact that every call sleeps for some number of milliseconds. On my
> system, the several hundred total msleep() calls can't cause any real
> overhead, and almost all happen at initialization time.
I'd be surprised if there was significant overhead - the maximum frequency
at which msleep() can be called is 1000Hz. We'd need an awful lot of
overhead for that to cause problems, surely?
<thinks he's missing something again>
next prev parent reply other threads:[~2007-08-07 19:40 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-03 18:37 [PATCH] msleep() with hrtimers Jonathan Corbet
2007-08-03 18:54 ` Ingo Molnar
2007-08-03 19:19 ` Roman Zippel
2007-08-03 19:46 ` Arjan van de Ven
2007-08-03 19:58 ` Roman Zippel
2007-08-03 23:53 ` Arjan van de Ven
2007-08-04 3:00 ` Roman Zippel
2007-08-04 19:19 ` Arjan van de Ven
2007-08-06 0:09 ` Roman Zippel
2007-08-06 0:43 ` Arjan van de Ven
2007-08-06 1:03 ` Roman Zippel
2007-08-06 5:39 ` Arjan van de Ven
2007-08-06 10:03 ` Roman Zippel
2007-08-06 10:20 ` Manu Abraham
2007-08-06 15:53 ` Arjan van de Ven
2007-08-07 10:40 ` Manu Abraham
2007-08-07 12:45 ` Roman Zippel
2007-08-08 4:15 ` Arjan van de Ven
2007-08-09 19:31 ` Denis Vlasenko
2007-08-09 20:01 ` Denis Vlasenko
2007-08-07 19:40 ` Andrew Morton [this message]
2007-08-07 23:16 ` Roman Zippel
2007-08-07 23:29 ` Andrew Morton
2007-08-08 3:47 ` Roman Zippel
2007-08-08 4:14 ` Andrew Morton
2007-08-09 22:31 ` Roman Zippel
2007-08-08 11:55 ` Andi Kleen
2007-08-08 11:09 ` Manu Abraham
2007-08-08 11:52 ` Andi Kleen
2007-08-08 11:59 ` Manu Abraham
2007-08-09 7:16 ` Andrew Morton
2007-08-09 15:08 ` [linux-usb-devel] " Alan Stern
2007-11-28 10:29 ` Andrew Morton
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