Re: [PATCH V3 for-next 1/3] IB/uverbs: Enable device removal when there are active user space applications

[Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

[-- Attachment #1: Type: text/plain, Size: 1504 bytes --]

On Thu, 2015-05-28 at 00:36 +0300, Or Gerlitz wrote:
> On Wed, May 27, 2015 at 8:43 PM, Jason Gunthorpe
> <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> wrote:
> > On Wed, May 27, 2015 at 12:04:29PM -0400, Doug Ledford wrote:
> >> On Mon, 2015-05-25 at 10:54 -0600, Jason Gunthorpe wrote:
> >> > On Wed, May 13, 2015 at 02:10:36PM +0300, Yishai Hadas wrote:
> >> >
> >> > > + struct srcu_struct                      disassociate_srcu;
> >> >
> >> > There is no need for rcu for this, use a rw sem.
> >>
> >> The rcu was used becuase it's on the hot path I assume.
> >
> > Perhaps, I looked at that a bit, it was used on syscall paths, but
> > that wasn't even the big reason I made the comment..
> 
> Doug, what hot path we have in uverbs?! IB's stack hot path goes from
> user-space to the HW, right?
> 
> Or.

For lots of stuff, yes.  However, the function that they picked this for
is ib_uverbs_write() and for certain things, that is a hot path.
Examples would be things like the cmtime test program in librdmacm, and
let's not forget that the whole reason that program was written was
because we were chasing an issue that caused real world applications to
fall over when they couldn't handle roughly 900 reverse route
resolutions per second, so I consider the cmtime utility, and the
stack's responsiveness to it, a valid item to optimize for.

-- 
Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
              GPG KeyID: 0E572FDD


[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 819 bytes --]