lkml.org 
[lkml]   [2015]   [Nov]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 0/2] "big hammer" for DAX msync/fsync correctness
    On Thu, 5 Nov 2015, Dan Williams wrote:
    > On Wed, Oct 28, 2015 at 3:51 PM, Ross Zwisler
    > <ross.zwisler@linux.intel.com> wrote:
    > > On Wed, Oct 28, 2015 at 06:24:29PM -0400, Jeff Moyer wrote:
    > >> Ross Zwisler <ross.zwisler@linux.intel.com> writes:
    > >>
    > >> > This series implements the very slow but correct handling for
    > >> > blkdev_issue_flush() with DAX mappings, as discussed here:
    > >> >
    > >> > https://lkml.org/lkml/2015/10/26/116
    > >> >
    > >> > I don't think that we can actually do the
    > >> >
    > >> > on_each_cpu(sync_cache, ...);
    > >> >
    > >> > ...where sync_cache is something like:
    > >> >
    > >> > cache_disable();
    > >> > wbinvd();
    > >> > pcommit();
    > >> > cache_enable();
    > >> >
    > >> > solution as proposed by Dan because WBINVD + PCOMMIT doesn't guarantee that
    > >> > your writes actually make it durably onto the DIMMs. I believe you really do
    > >> > need to loop through the cache lines, flush them with CLWB, then fence and
    > >> > PCOMMIT.
    > >>
    > >> *blink*
    > >> *blink*
    > >>
    > >> So much for not violating the principal of least surprise. I suppose
    > >> you've asked the hardware folks, and they've sent you down this path?
    > >
    > > Sadly, yes, this was the guidance from the hardware folks.
    >
    > So it turns out we weren't asking the right question. wbinvd may
    > indeed be viable... we're still working through the caveats.

    Just for the record. Such a flush mechanism with

    on_each_cpu()
    wbinvd()
    ...

    will make that stuff completely unusable on Real-Time systems. We've
    been there with the big hammer approach of the intel graphics
    driver.

    Thanks,

    tglx


    \
     
     \ /
      Last update: 2015-11-06 09:21    [W:2.382 / U:0.072 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site