On Fri, Sep 17, 2010 at 03:33:07PM +0530, Krishna Kumar wrote:
> For 1 TCP netperf, I ran 7 iterations and summed it. Explanation
> for degradation for 1 stream case:
Could you document how exactly do you measure multistream bandwidth:
netperf flags, etc?
> 1. Without any tuning, BW falls -6.5%.
Any idea where does this come from?
Do you see more TX interrupts? RX interrupts? Exits?
Do interrupts bounce more between guest CPUs?
> 2. When vhosts on server were bound to CPU0, BW was as good
> as with original code.
> 3. When new code was started with numtxqs=1 (or mq=off, which
> is the default), there was no degradation.
>
> Next steps:
> -----------
> 1. MQ RX patch is also complete - plan to submit once TX is OK (as
> well as after identifying bandwidth degradations for some test
> cases).
> 2. Cache-align data structures: I didn't see any BW/SD improvement
> after making the sq's (and similarly for vhost) cache-aligned
> statically:
> struct virtnet_info {
> ...
> struct send_queue sq[16] ____cacheline_aligned_in_smp;
> ...
> };
> 3. Migration is not tested.
4. Identify reasons for single netperf BW regression.
5. Test perf in more scenarious:
small packets
host -> guest
guest <-> external
in last case:
find some other way to measure host CPU utilization,
try multiqueue and single queue devices
6. Use above to figure out what is a sane default for numtxqs.
>
> Review/feedback appreciated.
>
> Signed-off-by: Krishna Kumar <krkumar2@xxxxxxxxxx>
> ---
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