lkml.org 
[lkml]   [2011]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)
    On Tue, Aug 23, 2011 at 03:15:58PM -0400, H. Peter Anvin wrote:
    > Right, but if you had said the difference had disappeared on current AMD
    > silicon it would be much less of an issue. That's why I wanted to find
    > that bit out from you.

    Yeah, I dug this out in the APM, btw.

    But no, I don't think the difference has disappeared - to the contrary,
    AFAICT, the intention is for SYSCALL to be the fastest way to do
    syscalls on x86 due to diminished number of segment checks etc. INT80
    is legacy, slower, etc. I believe Andy measured a similar situation on
    Sandy Bridge with SYSCALL having latencies in the tens of nsecs range
    and INT80 being much slower. Ingo also measured a similar situation
    where the latency gap between the two on Intel is even bigger.

    So, the only problem left now is what we're going
    to do with cases similar to what Al conjured up:
    http://marc.info/?l=linux-kernel&m=131412271112461&w=2

    I don't know, maybe the most cowardly approach is to issue a warning and
    shrug with the shoulders, or do some asm magic... Also, do we care at
    all, how relevant is a case like that?

    Hmmm.

    --
    Regards/Gruss,
    Boris.

    Advanced Micro Devices GmbH
    Einsteinring 24, 85609 Dornach
    GM: Alberto Bozzo
    Reg: Dornach, Landkreis Muenchen
    HRB Nr. 43632 WEEE Registernr: 129 19551


    \
     
     \ /
      Last update: 2011-08-23 22:59    [W:2.611 / U:0.120 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site