On Mon, 16 Mar 2015 19:58:51 +0000 "Dumitrescu, Cristian" <cristian.dumitrescu at intel.com> wrote:
> > > > -----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. > If you really wanted a fast/safe read and clear operation, how about using exchange instruction to exchange in a zero?
