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    SubjectRe: Kernel oops with 2.6.26, padlock and ipsec: probably problem with fpu state changes
    On Mon, Aug 11, 2008 at 12:24:59PM -0700, H. Peter Anvin wrote:
    > Ingo Molnar wrote:
    > > * Suresh Siddha <suresh.b.siddha@intel.com> wrote:
    > >
    > >> Reported-and-bisected-by: Wolfgang Walter <wolfgang.walter@stwm.de>
    > >> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
    > >
    > > no fundamental objection to the x86 bits.
    > >
    > > shouldnt this:
    > >
    > > + if (!in_interrupt())
    > > + return 0;
    > >
    > > just be eliminated and the cr0/TS save/restore be made unconditional?
    > > irq-assymetric APIs are not nice in general.
    > >
    > > Reading/setting cr0 isnt _that_ slow. (or if it is, by how much does it
    > > slow things down, exactly?)
    > >
    >
    > Setting it is relatively slow. I think that's part of the reason for
    > special instructions to muck with the TS flag.
    >
    > Reading it might be slow on obsolete processors.

    In addition to the slowness(Wolf has collected some data with earlier
    patch and I think it showed a double digit increase in cpu utilization with
    some crypt tests):

    we can't unconditionally do clts() in the process context. We have
    to disable pre-emption to avoid interactions with context switch and
    lazy restore. So there will be RT latency issues aswell.

    thanks,
    suresh


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