Re: [patch V2 00/20] timer: Refactor the timer wheel

From: Eric Dumazet
Date: Fri Jun 17 2016 - 09:48:47 EST


>
> To achieve this capacity with HZ=1000 without increasing the storage size
> by another level, we reduced the granularity of the first wheel level from
> 1ms to 4ms. According to our data, there is no user which relies on that
> 1ms granularity and 99% of those timers are canceled before expiry.
>

Ah... This might be a problem for people using small TCP RTO timers in
datacenters (order of 5 ms)
(and small delay ack timers as well, in the order of 4 ms)

TCP/pacing uses high resolution timer in sch_fq.c so no problem there.

If we arm a timer for 5 ms, what are the exact consequences ?

I fear we might trigger lot more of spurious retransmits.

Or maybe I should read the patch series. I'll take some time today.

Thanks !