lkml.org 
[lkml]   [2013]   [Sep]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface
    On Wed, Sep 25, 2013 at 05:00:16PM -0400, Tejun Heo wrote:
    > Hello,
    >
    > On Wed, Sep 25, 2013 at 10:58:05PM +0200, Alexander Gordeev wrote:
    > > Unfortunately, pSeries is a shows-topper here :( It seems we have to
    > > introduce pci_get_msi{,x}_limit() interfaces to honour the quota
    > > thing. I just hope the hardware set for pSeries is limited and we
    > > won't need to use it for all drivers.
    >
    > Can you please go into a bit of detail on that? Why does it matter?

    Because otherwise we will re-introduce a problem described by Michael:
    "We have a small number of MSIs available, limited by hardware &
    firmware, if we don't impose a quota then the first device that probes
    will get most/all of the MSIs and other devices miss out."

    > Is it because you're worried you might cause performance regression by
    > forcing prevoius partial multiple allocations to single interrupt
    > operation?

    Well, not really. I think it won't be possible to force people not to use
    partial allocations anyway. Some controllers just do not care how many MSIs
    they are configured with. Some drivers derive the number of MSIs desired
    from the number of CPUs online - in such cases allocating more MSIs (i.e.
    a number the controller advertised) could cause a performance degradation
    even.

    So when driver authors will know/measure/believe their hardware performs
    better with partial allocations they will stand for it. What we can do is
    to prevent those try-and-decrease fallbacks.

    > Thanks.
    >
    > --
    > tejun

    --
    Regards,
    Alexander Gordeev
    agordeev@redhat.com


    \
     
     \ /
      Last update: 2013-09-26 10:21    [W:5.018 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site