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Date: Sat, 11 Jun 2016 18:02:57 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: "Huang, Ying" <ying.huang@...el.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Rik van Riel <riel@...hat.com>, Michal Hocko <mhocko@...e.com>, LKML <linux-kernel@...r.kernel.org>, Michal Hocko <mhocko@...nel.org>, Minchan Kim <minchan@...nel.org>, Vinayak Menon <vinmenon@...eaurora.org>, Mel Gorman <mgorman@...e.de>, Andrew Morton <akpm@...ux-foundation.org>, LKP <lkp@...org> Subject: Re: [LKP] [lkp] [mm] 5c0a85fad9: unixbench.score -6.3% regression On Sat, Jun 11, 2016 at 5:49 PM, Huang, Ying <ying.huang@...el.com> wrote: > > From perf profile, the time spent in page_fault and its children > functions are almost same (7.85% vs 7.81%). So the time spent in page > fault and page table operation itself doesn't changed much. So, you > mean CPU may be slower to load the page table entry to TLB if accessed > bit is not set? So the CPU does take a microfault internally when it needs to set the accessed/dirty bit. It's not architecturally visible, but you can see it when you do timing loops. I've timed it at over a thousand cycles on at least some CPU's, but that's still peanuts compared to a real page fault. It shouldn't be *that* noticeable, ie no way it's a 6% regression on its own. Linus
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