Messages in this thread | | | Subject | RE: 2.6.25.4-rt2 | Date | Tue, 20 May 2008 08:44:42 +0800 | From | "MA QING A" <> |
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Forgive me to ask a stupid question. Why using the 24 mainline kernel, the time is less than using the rt-patched kernel?
-----Original Message----- From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Steven Rostedt Sent: 2008年5月20日 7:44 To: Kasper Sandberg Cc: LKML; RT; Ingo Molnar; Thomas Gleixner Subject: Re: 2.6.25.4-rt2
On Tue, 20 May 2008, Kasper Sandberg wrote:
> On Mon, 2008-05-19 at 18:43 -0400, Steven Rostedt wrote: > > We are pleased to announce the 2.6.25.4-rt2 tree, which can be
> Forgive me if i ask an obvious stupid question. But what is the status > of this -rt tree for .25 in relation with the BKL stuff?
Well, the BKL is still a semaphore in 25.
For my hackbench runs, I have:
[root@bxrhel51 c]# cat hack-test-2.6.25.4-rt2 Time: 4.937 Time: 4.842 Time: 4.877 Time: 4.905 Time: 4.924 Time: 4.781 Time: 4.927 Time: 4.871 Time: 5.181 Time: 4.866
Which is a bit slower than 2.6.24.7-rt7:
[root@bxrhel51 c]# cat hack-test-2.6.24.7-rt7 Time: 4.789 Time: 4.824 Time: 4.807 Time: 4.867 Time: 4.802 Time: 4.799 Time: 4.823 Time: 4.855 Time: 4.873 Time: 4.833
But then I checked the base kernels themselves:
[root@bxrhel51 c]# cat hack-test-2.6.24.7 Time: 3.817 Time: 3.921 Time: 3.887 Time: 3.920 Time: 3.874 Time: 3.858 Time: 3.912 Time: 3.926 Time: 3.888 Time: 3.901
[root@bxrhel51 c]# cat hack-test-2.6.25.4 Time: 6.225 Time: 6.319 Time: 6.257 Time: 6.534 Time: 6.077 Time: 6.787 Time: 6.927 Time: 6.218 Time: 5.929 Time: 6.554
Where there's a regression somewhere. For 25, the RT patch is actually *better* than mainline!
So I was thinking it had to do with the BKL regression, and then I ran:
[root@bxrhel51 c]# cat hack-test-2.6.26-rc3 Time: 6.789 Time: 7.123 Time: 6.197 Time: 5.496 Time: 6.708 Time: 5.609 Time: 6.679 Time: 6.206 Time: 6.351 Time: 5.969
Here it is no better, and the BKL has been converted into a spin lock.
But I'm very much busy working on -rt right now to dig deeper into this regression.
-- Steve
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