On 4/17/2014 4:55 PM, Chuck Lever wrote:
On Apr 17, 2014, at 3:06 AM, Sagi Grimberg <sa...@dev.mellanox.co.il> wrote:
On 4/16/2014 9:21 PM, Chuck Lever wrote:
Passing a small array to ip_poll_cq() is actually easy to do, and is
exactly equivalent to a poll budget. The struct ib_wc should be taken
off the stack anyway, IMO.
The only other example I see in 3.15 right now is IPoIB, which seems
to do exactly this.
I’m testing a patch now. I’d like to start simple and make it more
complex only if we need to.
What array size are you using? Note that if you use a small array it may be an
overkill since
a lot more interrupts are invoked (-> more latency). I found that for a high
workload a budget
of 256/512/1024 keeps fairness and doesn't increase latency.
My array size is currently 4. It’s a macro that can be changed easily.
By a very large majority, my workloads see only one WC per completion
upcall. However, I’m using an older card with simple synthetic benchmarks.
It doesn't matter until it does matter...
We noticed this phenomenon under *extreme* stress.
I don’t want to make the array large because struct ib_wc is at least
64 bytes on my systems — each WC array would be enormous and hardly ever
used.
Right, large WC array would be annoying...
Sagi.
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