Re: [PATCH v5 00/21] KVM: ARM64: Add guest PMU support

[Marc Zyngier <marc.zyngier@arm.com>]

Shannon,

On 03/12/15 06:11, Shannon Zhao wrote:
> From: Shannon Zhao <shannon.zhao@linaro.org>
> 
> This patchset adds guest PMU support for KVM on ARM64. It takes
> trap-and-emulate approach. When guest wants to monitor one event, it
> will be trapped by KVM and KVM will call perf_event API to create a perf
> event and call relevant perf_event APIs to get the count value of event.
> 
> Use perf to test this patchset in guest. When using "perf list", it
> shows the list of the hardware events and hardware cache events perf
> supports. Then use "perf stat -e EVENT" to monitor some event. For
> example, use "perf stat -e cycles" to count cpu cycles and
> "perf stat -e cache-misses" to count cache misses.
> 
> Below are the outputs of "perf stat -r 5 sleep 5" when running in host
> and guest.
> 
> Host:
>  Performance counter stats for 'sleep 5' (5 runs):
> 
>           0.510276      task-clock (msec)         #    0.000 CPUs utilized            ( +-  1.57% )
>                  1      context-switches          #    0.002 M/sec
>                  0      cpu-migrations            #    0.000 K/sec
>                 49      page-faults               #    0.096 M/sec                    ( +-  0.77% )
>            1064117      cycles                    #    2.085 GHz                      ( +-  1.56% )
>    <not supported>      stalled-cycles-frontend
>    <not supported>      stalled-cycles-backend
>             529051      instructions              #    0.50  insns per cycle          ( +-  0.55% )
>    <not supported>      branches
>               9894      branch-misses             #   19.390 M/sec                    ( +-  1.70% )
> 
>        5.000853900 seconds time elapsed                                          ( +-  0.00% )
> 
> Guest:
>  Performance counter stats for 'sleep 5' (5 runs):
> 
>           0.642456      task-clock (msec)         #    0.000 CPUs utilized            ( +-  1.81% )
>                  1      context-switches          #    0.002 M/sec
>                  0      cpu-migrations            #    0.000 K/sec
>                 49      page-faults               #    0.076 M/sec                    ( +-  1.64% )
>            1322717      cycles                    #    2.059 GHz                      ( +-  1.88% )
>    <not supported>      stalled-cycles-frontend
>    <not supported>      stalled-cycles-backend
>             640944      instructions              #    0.48  insns per cycle          ( +-  1.10% )
>    <not supported>      branches
>              10665      branch-misses             #   16.600 M/sec                    ( +-  2.23% )
> 
>        5.001181452 seconds time elapsed                                          ( +-  0.00% )
> 
> Have a cycle counter read test like below in guest and host:
> 
> static void test(void)
> {
> 	unsigned long count, count1, count2;
> 	count1 = read_cycles();
> 	count++;
> 	count2 = read_cycles();
> }
> 
> Host:
> count1: 3046186213
> count2: 3046186347
> delta: 134
> 
> Guest:
> count1: 5645797121
> count2: 5645797270
> delta: 149
> 
> The gap between guest and host is very small. One reason for this I
> think is that it doesn't count the cycles in EL2 and host since we add
> exclude_hv = 1. So the cycles spent to store/restore registers which
> happens at EL2 are not included.
> 
> This patchset can be fetched from [1] and the relevant QEMU version for
> test can be fetched from [2].
> 
> The results of 'perf test' can be found from [3][4].
> The results of perf_event_tests test suite can be found from [5][6].
> 
> Also, I have tested "perf top" in two VMs and host at the same time. It
> works well.

I've commented on more issues I've found. Hopefully you'll be able to
respin this quickly enough, and end-up with a simpler code base (state
duplication is a bit messy).

Another thing I have noticed is that you have dropped the vgic changes
that were configuring the interrupt. It feels like they should be
included, and configure the PPI as a LEVEL interrupt. Also, looking at
your QEMU code, you seem to configure the interrupt as EDGE, which is
now how yor emulated HW behaves.

Looking forward to reviewing the next version.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...