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Message-ID: <20120222011652.GE23186@zod.bos.redhat.com> Date: Tue, 21 Feb 2012 20:16:53 -0500 From: Josh Boyer <jwboyer@...hat.com> To: paulmck@...ux.vnet.ibm.com Cc: linux-kernel@...r.kernel.org, kernel-team@...oraproject.org Subject: Large slowdown with 'x86: Avoid invoking RCU when CPU is idle' Hi Paul, Over in Fedora land, I applied your patch from this thread: https://lkml.org/lkml/2012/1/24/441 to our 3.3-rc3/rc4 based rawhide kernels. The intention was to solve an RCU issue that was very similar to what Eric originally reported, and the RCU splat did indeed go away[1]. However, we then got a few reports of kernels containing that patch being extremely slow. When the patch was dropped, the slowness goes away according to one reporter. The details can be found in this bug: https://bugzilla.redhat.com/show_bug.cgi?id=795050 The slowness doesn't seem to hit everyone, and in my local testing things seem to be working just fine. The reporters have widely varying hardware as well, so it doesn't seem machine specific. Perhaps I misdiagnosed the original issue, or perhaps I missed something else that needs to be applied prior to this but I thought I would point this out in case you had any ideas. josh [1] https://bugzilla.redhat.com/show_bug.cgi?id=789641 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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