lkml.org 
[lkml]   [2008]   [Aug]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected
    Date
    On Wednesday 27 August 2008 17:05, David Miller wrote:
    > From: Nick Piggin <nickpiggin@yahoo.com.au>
    > Date: Wed, 27 Aug 2008 16:54:32 +1000
    >
    > > 5% is a pretty nasty performance hit... what sort of benchmarks are we
    > > talking about here?
    > >
    > > I just made some pretty crazy changes to the VM to get "only" around 5
    > > or so % performance improvement in some workloads.
    > >
    > > What places are making heavy use of cpumasks that causes such a slowdown?
    > > Hopefully callers can mostly be improved so they don't need to use
    > > cpumasks for common cases.
    >
    > It's almost certainly from the cross-call dispatch call chain.
    >
    > As just one example, just to do a TLB flush mm->cpu_vm_mask probably
    > gets passed around as an aggregate two or three times on the way down
    > to the APIC programming code on x86. That's two or three 512 byte
    > copies on the stack :)

    Yeah, I see. That's stupid isn't it? (Well, I guess it was completely
    sane when cpumasks were word sized ;))

    Hopefully that accounts for a significant chunk...


    \
     
     \ /
      Last update: 2008-08-27 09:51    [W:4.114 / U:0.596 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site