[PATCH] Add the VSL tag BereqEnd

Geoff Simmons geoff at uplex.de
Wed Oct 23 17:03:29 CEST 2013


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On 10/23/2013 02:33 PM, Poul-Henning Kamp wrote:
> 
> The writev() to the kernel doesn't happen until WRW_FlushRelease(), so
> at the very least the timestamp should be taken after that.

OK

> But...
> 
> The time you measure is only the time to hand the request to the kernels
> network stack.  As far as I know, there is no way to wait on a socket
> until all queued data has been sent (or even ACKed).

Yes. In my tests, the value was always in the µs range, altogether
dwarfed by the other two deltas. Even in the best case, it will probably
be the one that users will be least interested in.

Martin suggested adding tReq to help find out if there are network
latencies that slow down requests getting to backends in the first place
(or slow down pipes). That would be good to know, but if there's no way
to actually measure it within varnishd, we should re-consider having it
at all.


Best,
Geoff
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