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SubjectRe: [net-next RFC V5 0/5] Multiqueue virtio-net
On 07/07/2012 12:23 AM, Rick Jones wrote:
> On 07/06/2012 12:42 AM, Jason Wang wrote:
>> I'm not expert of tcp, but looks like the changes are reasonable:
>> - we can do full-sized TSO check in tcp_tso_should_defer() only for
>> westwood, according to tcp westwood
>> - run tcp_tso_should_defer for tso_segs = 1 when tso is enabled.
> I'm sure Eric and David will weigh-in on the TCP change. My initial
> inclination would have been to say "well, if multiqueue is draining
> faster, that means ACKs come-back faster, which means the "race"
> between more data being queued by netperf and ACKs will go more to the
> ACKs which means the segments being sent will be smaller - as
> TCP_NODELAY is not set, the Nagle algorithm is in force, which means
> once there is data outstanding on the connection, no more will be sent
> until either the outstanding data is ACKed, or there is an
> accumulation of > MSS worth of data to send.
>>> Also, how are you combining the concurrent netperf results? Are you
>>> taking sums of what netperf reports, or are you gathering statistics
>>> outside of netperf?
>> The throughput were just sumed from netperf result like what netperf
>> manual suggests. The cpu utilization were measured by mpstat.
> Which mechanism to address skew error? The netperf manual describes
> more than one:

This mechanism is missed in my test, I would add them to my test scripts.
> Personally, my preference these days is to use the "demo mode" method
> of aggregate results as it can be rather faster than (ab)using the
> confidence intervals mechanism, which I suspect may not really scale
> all that well to large numbers of concurrent netperfs.

During my test, the confidence interval would even hard to achieved in
RR test when I pin vhost/vcpus in the processors, so I didn't use it.
> I also tend to use the --enable-burst configure option to allow me to
> minimize the number of concurrent netperfs in the first place. Set
> TCP_NODELAY (the test-specific -D option) and then have several
> transactions outstanding at one time (test-specific -b option with a
> number of additional in-flight transactions).
> This is expressed in the script:
> which uses the script:
> to pick the burst size to use in the concurrent netperfs, the results
> of which can be post-processed with:
> The nice feature of using the "demo mode" mechanism is when it is
> coupled with systems with reasonably synchronized clocks (eg NTP) it
> can be used for many-to-many testing in addition to one-to-many
> testing (which cannot be dealt with by the confidence interval method
> of dealing with skew error)

Yes, looks "demo mode" is helpful. I would have a look at these scripts,
>>> A single instance TCP_RR test would help confirm/refute any
>>> non-trivial change in (effective) path length between the two cases.
>> Yes, I would test this thanks.
> Excellent.
> happy benchmarking,
> rick jones
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