On Wed, Feb 05, 2014 at 04:32:55PM -0800, Linus Torvalds wrote: > On Sun, Jan 26, 2014 at 2:28 PM, Linus Torvalds > <[email protected]> wrote: > > > > Comments? This was obviously brought on by my frustration with the > > currently nasty do_notify_resume() always returning to iret for the > > task_work case, and PeterZ's patch that fixed that, but made the asm > > mess even *worse*. > > Actually, I should have taken a closer look. > > Yes, do_notify_resume() is a real issue, and my stupid open/close > test-case showed that part of the profile. > > But the "iretq" that dominates on the kernel build is actually the > page fault one. > > I noticed this when I compared "-e cycles:pp" with "-e cycles:p". The > single-p version shows largely the same profile for the kernel, except > that instead of showing "iretq" as the big cost, it shows the first > instruction in "page_fault". > > In fact, even when *not* zoomed into the kernel DSO, "page_fault" > actually takes 5% of CPU time according to pref report. That's really > quite impressive. > > I suspect the Haswell architecture has made everything else cheaper, > and the exception overhead hasn't kept up. I'm wondering if there is > anything we could do to speed this up - like doing gang lookup in the > page cache and pre-populating the page tables opportunistically.
One thing that could help is THP for file-backed pages. And there's prototype with basic infrasturure and support for ramfs and shmem/tmpfs (by Ning Qu). Work in progress. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
