linux-kernel - Re: [PATCH v5 11/16] perf kvm: Use histograms list to replace cached list

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Date:   Thu, 16 Mar 2023 17:04:18 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        John Garry <john.g.garry@...cle.com>,
        James Clark <james.clark@....com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 11/16] perf kvm: Use histograms list to replace cached
 list

On Thu, Mar 16, 2023 at 12:42:53AM -0700, Namhyung Kim wrote:

[...]

> >  static struct kvm_event *find_create_kvm_event(struct perf_kvm_stat *kvm,
> >                                                struct event_key *key,
> >                                                struct perf_sample *sample)
> >  {
> >         struct kvm_event *event;
> > -       struct list_head *head;
> > +       struct hist_entry *he;
> > +       struct kvm_info *ki;
> >
> >         BUG_ON(key->key == INVALID_KEY);
> >
> > -       head = &kvm->kvm_events_cache[kvm_events_hash_fn(key->key)];
> > -       list_for_each_entry(event, head, hash_entry) {
> > -               if (event->key.key == key->key && event->key.info == key->info)
> > -                       return event;
> > +       ki = zalloc(sizeof(*ki));
> > +       if (!ki) {
> > +               pr_err("Failed to allocate kvm info\n");
> > +               return NULL;
> >         }
> >
> > -       event = kvm_alloc_init_event(kvm, key, sample);
> > -       if (!event)
> > +       kvm->events_ops->decode_key(kvm, key, ki->name);
> > +       he = hists__add_entry_ops(&kvm_hists.hists, &kvm_ev_entry_ops,
> > +                                 &kvm->al, NULL, NULL, NULL, ki, sample, true);
> 
> The hists__add_entry{,_ops} can return either a new entry
> or an existing one.  I think it'd leak the 'ki' when it returns
> the existing one.  You may deep-copy it in hist_entry__init()
> and always free the 'ki' here.

Thanks for pointing out this, Namhyung.  I will fix it.

@Arnaldo, do you want me to send an appending patch, or will you drop
this patch series from your branch so I send a new patch set?

> Another thought on this.  Lots of fields in the hist_entry are
> not used for kvm.  We might split the hist_entry somehow
> so that we can use unnecessary parts only.  But that could
> be a future project. :)

Yeah, I found now hist_entry contains many fields
(branch_info/mem_info/kvm_info/block_info); we can consider to
refactor the struct hist_entry to use an abstract pointer to refer
tool's specific data, this could be easily extend hist_entry to
support more tools.

Thanks,
Leo