Messages in this thread | | | Subject | Re: [PATCH v11 8/8] perf: ARM DynamIQ Shared Unit PMU support | From | Suzuki K Poulose <> | Date | Mon, 19 Mar 2018 09:50:18 +0000 |
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On 07/03/18 21:36, Saravana Kannan wrote: > On 03/07/2018 06:59 AM, Suzuki K Poulose wrote: >> >> >> Hi Saravana, >> >> Sorry for the late response, I was out on vacation. >> >> On 05/03/18 22:10, Saravana Kannan wrote: >>> On 03/05/2018 02:59 AM, Mark Rutland wrote: >>>> On Fri, Mar 02, 2018 at 11:19:56AM -0800, Saravana Kannan wrote: >>>>> On 03/02/2018 02:42 AM, Mark Rutland wrote: >>>>>> It's important to note that the DSU PMU's event_init() ensures events >>>>>> are affine to a single CPU, and the perf core code serializes >>>>>> operations >>>>>> on those events via the context lock. >>>>> >>>>> Ah, I see that now. Thanks! >>>>> >>>>>> Therefore, two CPUs *won't* try to access the registers >>>>>> simultaneously. >>>>> >>>>> Right, and this driver seems to be going through a lot of work to >>>>> make sure >>>>> all events are read in one CPU. >>>>> >>>>> Do you even have an upstream target where there are multiple DSU's in a >>>>> system? >>>> >>>> I have no idea, though I do beleive that it's possible for a system to >>>> have multiple DSUs. >>>> >>>>> If not, we can simplify a ton of this code (no hotplug notifiers, no >>>>> migrating PMUs, no SMP calls, etc) by just adding a spinlock and >>>>> letting any >>>>> CPU read these DSU counters. >>>> >>>> Regardless of whether we allow arbitrary CPUs to read the counters, >>>> other logic still needs to be CPU affine, and we'll still need hotplug >>>> notifiers and event migration. >>> >>> If you have to support multiple DSUs in a system, then the need is >>> obvious. But if you don't have to support multiple DSU, it's not >>> obvious to me on why you still need CPU affining or hotplug notifiers. >>> Could you please provide me pointers for general understanding? >>> >> >> We need to support multiple DSUs as such configurations are possible. >> >>> >>>> I am not necessarily opposed to allowing read() calls from associated >>>> CPUs, but as before, I'll leave that to Suzuki. >> >> I am fine with reading the registers from any of the associated CPUs. >> > > If that's the case, can you please use my patch?
The DSU driver is already mainline. Please feel free to send a patch with me in Cc.
> And if it looks good to you, give an Ack and ask Peter to pull it in as you'd be the user?
As mentioned above, when you send a patch, please do keep me in Cc, and will do the needful.
Thanks Suzuki
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