David Mosberger wrote:
The problems started with 2.6.10-bk7...On Tue, 05 Apr 2005 20:11:51 +0200, Andreas Hirstius <[EMAIL PROTECTED]> said:
Andreas> Hi, We have a rx4640 with 3x 3Ware 9500 SATA controllers Andreas> and 24x WD740GD HDD in a software RAID0 configuration Andreas> (using md). With kernel 2.6.11 the read performance on the Andreas> md is reduced by a factor of 20 (!!) compared to previous Andreas> kernels. The write rate to the md doesn't change!! (it Andreas> actually improves a bit).
Is there any reason to believe this change in behavior is ia64-specific? I doubt it. The q-syscollect profiles on your web-site shows that the CPU is basically completely idle. You may want to try 2.6.10 to see whether the bad behavior was introduced before or after that. Unfortunately, 2.6 is developing very rapidly so you may have to do more binary searching between 2.6.9 and 2.6.10 or 2.6.10 and 2.6.11 to pin the problem down to a useful granularity. You may also want to look at the bitkeeper changelogs to see if you can find anything suspicious (you can do that easily via the web by browsing the source code [1]). Lastly, you may want to ask on linux-kernel whether anybody can think of a change that could have this effect.
(and I've tested 2.6.9, 2.6.10, 2.6.10-bk5 - -bk14, 2.6.11-rc[1-5], 2.6.11, 2.6.11-mm[12], 2.6.12-rc[12])
The only other platform I have is a dual-xeon and I don't see the problem there (same controllers/disks)...
Because of this strange correlation between block size and page size and the fact, that I don't see a problem on x86 I suspected an ia64-specific problem. My "favourite" candidate is the conversion to 4 level pagetables between 2.6.10-bk6 and 2.6.10-bk7.
Andreas
--david
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