linux-kernel - Re: [PATCH v6 07/11] drivers: perf: hisi: Add support for Hisilicon SoC event counters

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Date:   Fri, 31 Mar 2017 15:23:52 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Anurup M <anurupvasu@...il.com>
Cc:     will.deacon@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, anurup.m@...wei.com,
        zhangshaokun@...ilicon.com, tanxiaojun@...wei.com,
        xuwei5@...ilicon.com, sanil.kumar@...ilicon.com,
        john.garry@...wei.com, gabriele.paoloni@...wei.com,
        shiju.jose@...wei.com, huangdaode@...ilicon.com,
        linuxarm@...wei.com, dikshit.n@...wei.com, shyju.pv@...wei.com
Subject: Re: [PATCH v6 07/11] drivers: perf: hisi: Add support for Hisilicon
 SoC event counters

On Fri, Mar 31, 2017 at 07:43:20PM +0530, Anurup M wrote:
> On Thursday 30 March 2017 04:16 PM, Mark Rutland wrote:
> >>>>>+	/*
> >>>>>> >>>+	 * We must NOT create groups containing mixed PMUs, although
> >>>>>> >>>+	 * software events are acceptable
> >>>>>> >>>+	 */
> >>>>>> >>>+	if (event->group_leader->pmu != event->pmu &&
> >>>>>> >>>+	    !is_software_event(event->group_leader))
> >>>>>> >>>+		return -EINVAL;
> >>>>>> >>>+
> >>>>>> >>>+	list_for_each_entry(sibling, &event->group_leader->sibling_list,
> >>>>>> >>>+			    group_entry)
> >>>>>> >>>+		if (sibling->pmu != event->pmu && !is_software_event(sibling))
> >>>>>> >>>+			return -EINVAL;
> >>>> >Please also check the number of counters.
> >>>
> >>>Sorry, I could not follow this comment correctly. Could you please explain ?
> >>>I check the available counters and update used mask in pmu_add -->
> >>>get_event_index
> >What I meant was that here we should ensure that a group does not
> >contain more events than can fit into counters.
> >
> >For example, if the HW had two counters, we should reject any group with
> >more than two events. Such groups can never be scheduled, and make no
> >sense.
> 
> I have referred drivers/bus/arm-cci.c and could find validate_group
> and validate_event functions,
> which create a fake_pmu to check the available counters for the
> events in the group.
> Is that the same way which is expected here? Please comment.

Something like that.

I think it's simplest to have a validate_group() function, which counts
the number of counters used. See my suggestion in [1].

Thanks,
Mark.

[1] https://lkml.kernel.org/r/20170331135955.GB6488@leverpostej