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Date: Fri, 13 May 2011 11:12:36 -0500 From: James Bottomley <James.Bottomley@...senPartnership.com> To: x86@...nel.org Cc: linux-mm <linux-mm@...ck.org>, linux-kernel <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de> Subject: Possible sandybridge livelock issue We've just come off a large round of debugging a kswapd problem over on linux-mm: http://marc.info/?t=130392066000001 The upshot was that kswapd wasn't being allowed to sleep (which we're now fixing). However, in spite of intensive efforts, the actual hang was only reproducible on sandybridge laptops. When the hang occurred, kswapd basically pegged one core in 100% system time. This looks like there's something specific to sandybridge that causes this type of bad interaction. I was wondering if it could be something to to with a scheduling problem in turbo mode? Once kswapd goes flat out, the core its on will kick into turbo mode, which causes it to get preferentially scheduled there, leading to the live lock. The only evidence I have to support this theory is that when I reproduce the problem with PREEMPT, the core pegs at 100% system time and stays there even if I turn off the load. However, if I can execute work that causes kswapd to be kicked off the core it's running on, it will calm back down and go to sleep. James -- 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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