> -----Original Message----- > From: Stephen Hemminger [mailto:stephen at networkplumber.org] > Sent: Thursday, March 12, 2015 11:06 PM > To: Dumitrescu, Cristian > Cc: dev at dpdk.org; Stephen Hemminger > Subject: Re: [PATCH v2 5/6] rte_sched: allow reading statistics without > clearing > > On Thu, 12 Mar 2015 19:28:11 +0000 > "Dumitrescu, Cristian" <cristian.dumitrescu at intel.com> wrote: > > > Hi Stephen, > > > > Thank you for adding flexibility over clearing the stats or not. > > > > I have one concern though: why change the stats read API to add a clear > parameter rather than keep prototype for the stats functions unchanged and > add the flag as part of the port creation parameters in struct > rte_sched_port_params? This parameter could be saved into the internal > struct rte_sched_port, which is passed (as a pointer) to the stats read > functions. In my opinion, this approach is slightly more elegant and it keeps > the changes to a minimum. > > > > int > > rte_sched_queue_read_stats(struct rte_sched_port *port, > > uint32_t queue_id, > > struct rte_sched_queue_stats *stats, > > uint16_t *qlen) > > { > > ... > > if (port->clear_stats_on_read) > > memset(...); > > } > > > > I made this suggestion during the previous round, but I did not get any > opinion from you on it yet. > > > > Regards, > > Cristian > > I rejected the config parameter idea because I don't like it is inconsistent > with other statistics in DPDK and in related software. There is not a > config parameter that changes what BSD or Linux kernel API does.
Your approach has the advantage of being able to clear/not clear the stats per each read operation rather than configuring the behavior globally. I think this approach allows for the ultimate flexibility, so I am OK to go with it. > > The only reason for keeping the read and clear in one operation is > because you like it, and there are somebody might have built code > that expects it. > Clearing the stats with a delay after the stats have been read is prone to a race condition, as during this time more packets could be processed, and these packets will not show up in the counters that the user read. I think it depends on the need of each particular application whether this race condition is important or not: if the counters are read rarely (e.g. once per day) and only course accuracy is required, the error is probably irrelevant; if the app is looking for fine great accuracy (e.g. rate measurement, debugging, etc), then the error is not allowed. You seem to favour the former and ignore the later case. > Changing the function signature is a nice red flag so that people will > notice at change. There is a small API change here. I am OK with it for the above reasons, provided that there are no objections on this from other contributors.
