Messages in this thread | | | Date | Sun, 27 Sep 2009 21:20:25 +0200 | From | Nick Piggin <> | Subject | Re: [RFC][PATCH] HWPOISON: remove the unsafe __set_page_locked() |
| |
On Sun, Sep 27, 2009 at 06:47:39PM +0800, Wu Fengguang wrote: > > > > And standard deviation is 0.04%, much larger than the difference 0.008% .. > > Sorry that's not correct. I improved the accounting by treating > function0+function1 from two CPUs as an integral entity: > > total time add_to_page_cache_lru percent stddev > before 3880166848.722 9683329.610 0.250% 0.014% > after 3828516894.376 9778088.870 0.256% 0.012% > delta 0.006%
I don't understand why you're doing this NFS workload to measure? I see significant nfs, networking protocol and device overheads in your profiles, also you're hitting some locks or something which is causing massive context switching. So I don't think this is a good test. But anyway as Hugh points out, you need to compare with a *completely* fixed kernel, which includes auditing all users of page flags non-atomically (slab, notably, but possibly also other places).
One other thing to keep in mind that I will mention is that I am going to push in a patch to the page allocator to allow callers to avoid the refcounting (atomic_dec_and_test) in page lifetime, which is especially important for SLUB and takes more cycles off the page allocator...
I don't know exactly what you're going to do after that to get a stable reference to slab pages. I guess you can read the page flags and speculatively take some slab locks and recheck etc...
| |