On Thu, 25 Apr 2024 00:27:36 +0200 Mattias Rönnblom <hof...@lysator.liu.se> wrote:
> On 2024-04-24 21:13, Stephen Hemminger wrote: > > On Wed, 24 Apr 2024 18:50:50 +0100 > > Ferruh Yigit <ferruh.yi...@amd.com> wrote: > > > >>> I don't know how slow af_packet is, but if you care about performance, > >>> you don't want to use atomic add for statistics. > >>> > >> > >> There are a few soft drivers already using atomics adds for updating stats. > >> If we document expectations from 'rte_eth_stats_reset()', we can update > >> those usages. > > > > Using atomic add is lots of extra overhead. The statistics are not > > guaranteed > > to be perfect. If nothing else, the bytes and packets can be skewed. > > > > The sad thing here is that in case the counters are reset within the > load-modify-store cycle of the lcore counter update, the reset may end > up being a nop. So, it's not like you missed a packet or two, or suffer > some transient inconsistency, but you completed and permanently ignored > the reset request. That is one of the many reasons the Linux kernel intentionally did not implement a reset statistics operation.
