On Fri, Apr 14, 2017 at 04:17:18PM +0300, Alexey Perevalov wrote:
[...]
> +/*
> + * This function calculates downtime per cpu and trace it
> + *
> + * Also it calculates total downtime as an interval's overlap,
> + * for many vCPU.
> + *
> + * The approach is following:
> + * Initially intervals are represented in tree where key is
> + * pagefault address, and values:
> + * begin - page fault time
> + * end - page load time
> + * cpus - bit mask shows affected cpus
> + *
> + * To calculate overlap on all cpus, intervals converted into
> + * array of points in time (downtime_points), the size of
> + * array is 2 * number of nodes in tree of intervals (2 array
> + * elements per one in element of interval).
> + * Each element is marked as end (E) or as start (S) of interval.
> + * The overlap downtime will be calculated for SE, only in case
> + * there is sequence S(0..N)E(M) for every vCPU.
> + *
> + * As example we have 3 CPU
> + *
> + * S1 E1 S1 E1
> + * -----***********------------xxx***************------------------------>
> CPU1
> + *
> + * S2 E2
> + * ------------****************xxx--------------------------------------->
> CPU2
> + *
> + * S3 E3
> + * ------------------------****xxx********------------------------------->
> CPU3
> + *
> + * We have sequence S1,S2,E1,S3,S1,E2,E3,E1
> + * S2,E1 - doesn't match condition due to sequence S1,S2,E1 doesn't include
> CPU3
> + * S3,S1,E2 - sequenece includes all CPUs, in this case overlap will be S1,E2
> + * Legend of picture is following: * - means downtime per vCPU
> + * x - means overlapped downtime
> + */
Not sure whether I get the point in this patch... iiuc we defined the
downtime here as the period when all vcpus are halted, right?
If so, I have a few questions:
- will this algorithm consume lots of memory? since I see we have one
trace object per fault page address
- do we need to protect the tree to make sure there's no insertion
when doing the calculation?
- if the only thing we want here is the "total downtime", whether
below would work? (assuming N is vcpu numbers)
a. define array cpu_fault_addr[N], to store current faulted address
for each vcpu. When vcpu X is running, cpu_fault_addr[X] should
be 0.
b. when page fault happens on vcpu A, setup cpu_fault_addr[A] with
corresponding fault address.
c. when page copy finished, loop over cpu_fault_addr[] to see
whether that matches any, clear corresponding element if matched.
Then, we can just measure the period when cpu_fault_addr[] is all
set (by tracing at both b. and c.). Can this work?
Thanks,
--
Peter Xu
