Re: [PATCH 00/11] New Caching mechanism for ib_core

Goldwyn Rodrigues
2011-11-11T04:15:24Z

Hi Sean,

On Thu, Nov 10, 2011 at 07:03:40AM +0000, Hefty, Sean wrote:
> > > Yes, but the use of the cache is hidden from the user.
> >
> > user who?
>
> ib_cm, rdma_cm, ib_mad, ib_ipoib, etc. You would need to trace the use up to all ULPs.
>
> > Since the drivers would be users of cache calls, the behavior would be
> > as assumed for the query calls for the driver. Refer mthca
> > implementation (PATCH 11/11): If the entry is found in cache, it
> > will return immediately, and will not sleep.
>
> > If the entry is not found, it will query the device and may sleep.
>
> This is the issue. You changed calls from ib_find_cached_pkey() and ib_find_cached_gid() to ib_query_pkey() and ib_query_gid(). The latter calls may sleep, but I don't believe that we can sleep in all places where the new functions are used. Changing from ib_find_cached_gid to ib_query_gid changes the locking restrictions up through the stack. It doesn't matter if the cache doesn't block, the exposed calls may.

Thanks for explaining. I see your point now. This had been in the
orignal discussion, but I missed on this point while working
on this. I will redo the patches after reviewing the function usage.