[PATCH v4 1/1] qemu: add per-vcpu delay stats
Daniel Henrique Barboza
danielhb413 at gmail.com
Thu Mar 4 11:56:39 UTC 2021
On 2/19/21 5:08 PM, Aleksei Zakharov wrote:
> This patch adds delay time (steal time inside guest) to libvirt
> domain per-vcpu stats. Delay time is an important performance metric.
> It is a consequence of the overloaded CPU. Knowledge of the delay
> time of a virtual machine helps to understand if it is affected and
> estimate the impact.
>
> As a result, it is possible to react exactly when needed and
> rebalance the load between hosts. This is used by cloud providers
> to provide quality of service, especially when the CPU is
> oversubscribed.
>
> It's more convenient to work with this metric in a context of a
> libvirt domain. Any monitoring software may use this information.
>
> Signed-off-by: Aleksei Zakharov <zaharov at selectel.ru>
> ---
> docs/manpages/virsh.rst | 4 ++++
> src/libvirt-domain.c | 4 ++++
> src/qemu/qemu_driver.c | 44 +++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 50 insertions(+), 2 deletions(-)
>
> diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
> index e3afa48f7b..a2b83ddfaa 100644
> --- a/docs/manpages/virsh.rst
> +++ b/docs/manpages/virsh.rst
> @@ -2295,6 +2295,10 @@ When selecting the *--state* group the following fields are returned:
> * ``vcpu.<num>.halted`` - virtual CPU <num> is halted: yes or
> no (may indicate the processor is idle or even disabled,
> depending on the architecture)
> +* ``vcpu.<num>.delay`` - time the vCPU <num> thread was enqueued by the
> + host scheduler, but was waiting in the queue instead of running.
> + Exposed to the VM as a steal time.
> +
>
>
> *--interface* returns:
> diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
> index 4af0166872..e54d11e513 100644
> --- a/src/libvirt-domain.c
> +++ b/src/libvirt-domain.c
> @@ -11693,6 +11693,10 @@ virConnectGetDomainCapabilities(virConnectPtr conn,
> * "vcpu.<num>.halted" - virtual CPU <num> is halted, may indicate the
> * processor is idle or even disabled, depending
> * on the architecture)
> + * "vcpu.<num>.delay" - time the vCPU <num> thread was enqueued by the
> + * host scheduler, but was waiting in the queue
> + * instead of running. Exposed to the VM as a steal
> + * time.
> *
> * VIR_DOMAIN_STATS_INTERFACE:
> * Return network interface statistics (from domain point of view).
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index b9bbdf8d48..9ec3c8fce7 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -1332,6 +1332,34 @@ static char *qemuConnectGetCapabilities(virConnectPtr conn) {
> return virCapabilitiesFormatXML(caps);
> }
>
> +static int
> +qemuGetSchedstatDelay(unsigned long long *cpudelay,
> + pid_t pid, pid_t tid)
> +{
> + g_autofree char *proc = NULL;
> + unsigned long long oncpu = 0;
> + g_autofree FILE *schedstat = NULL;
So, the most common practice in the project is to declare the file fds with
VIR_AUTOCLOSE to avoid having to close the fd at the end. There are a lot of
examples in src/util/virnetdev.c. This is the first time I see
'g_autofree FILE *'.
> +
> + if (tid)
> + proc = g_strdup_printf("/proc/%d/task/%d/schedstat", (int)pid, (int)tid);
> + else
> + proc = g_strdup_printf("/proc/%d/schedstat", (int)pid);
> +
> + schedstat = fopen(proc, "r");
> + if (!schedstat) {
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + _("Unable to open schedstat file at '%s'"),
> + proc);
> + }
> + if (fscanf(schedstat, "%llu %llu", &oncpu, cpudelay) < 2) {
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + _("Unable to parse schedstat info at '%s'"),
> + proc);
> + }
> +
> + VIR_FORCE_FCLOSE(schedstat);
That said, reading the change log for the patch I see that someone already
mentioned the needed to close the FD in v1 and you fixed it in v2, so I'll
take that this code, albeit unusual to me, works. If it doesn't, it's a
rather trivial amend that the maintainer can do before pushing.
Reviewed-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
> + return 0;
> +}
>
> static int
> qemuGetSchedInfo(unsigned long long *cpuWait,
> @@ -1470,6 +1498,7 @@ static int
> qemuDomainHelperGetVcpus(virDomainObjPtr vm,
> virVcpuInfoPtr info,
> unsigned long long *cpuwait,
> + unsigned long long *cpudelay,
> int maxinfo,
> unsigned char *cpumaps,
> int maplen)
> @@ -1529,6 +1558,11 @@ qemuDomainHelperGetVcpus(virDomainObjPtr vm,
> return -1;
> }
>
> + if (cpudelay) {
> + if (qemuGetSchedstatDelay(&(cpudelay[ncpuinfo]), vm->pid, vcpupid) < 0)
> + return -1;
> + }
> +
> ncpuinfo++;
> }
>
> @@ -4873,7 +4907,7 @@ qemuDomainGetVcpus(virDomainPtr dom,
> goto cleanup;
> }
>
> - ret = qemuDomainHelperGetVcpus(vm, info, NULL, maxinfo, cpumaps, maplen);
> + ret = qemuDomainHelperGetVcpus(vm, info, NULL, NULL, maxinfo, cpumaps, maplen);
>
> cleanup:
> virDomainObjEndAPI(&vm);
> @@ -17934,6 +17968,7 @@ qemuDomainGetStatsVcpu(virQEMUDriverPtr driver,
> int ret = -1;
> virVcpuInfoPtr cpuinfo = NULL;
> g_autofree unsigned long long *cpuwait = NULL;
> + g_autofree unsigned long long *cpudelay = NULL;
>
> if (virTypedParamListAddUInt(params, virDomainDefGetVcpus(dom->def),
> "vcpu.current") < 0)
> @@ -17945,6 +17980,7 @@ qemuDomainGetStatsVcpu(virQEMUDriverPtr driver,
>
> cpuinfo = g_new0(virVcpuInfo, virDomainDefGetVcpus(dom->def));
> cpuwait = g_new0(unsigned long long, virDomainDefGetVcpus(dom->def));
> + cpudelay = g_new0(unsigned long long, virDomainDefGetVcpus(dom->def));
>
> if (HAVE_JOB(privflags) && virDomainObjIsActive(dom) &&
> qemuDomainRefreshVcpuHalted(driver, dom, QEMU_ASYNC_JOB_NONE) < 0) {
> @@ -17953,7 +17989,7 @@ qemuDomainGetStatsVcpu(virQEMUDriverPtr driver,
> virResetLastError();
> }
>
> - if (qemuDomainHelperGetVcpus(dom, cpuinfo, cpuwait,
> + if (qemuDomainHelperGetVcpus(dom, cpuinfo, cpuwait, cpudelay,
> virDomainDefGetVcpus(dom->def),
> NULL, 0) < 0) {
> virResetLastError();
> @@ -17978,6 +18014,10 @@ qemuDomainGetStatsVcpu(virQEMUDriverPtr driver,
> "vcpu.%u.wait", cpuinfo[i].number) < 0)
> goto cleanup;
>
> + if (virTypedParamListAddULLong(params, cpudelay[i],
> + "vcpu.%u.delay", cpuinfo[i].number) < 0)
> + goto cleanup;
> +
> /* state below is extracted from the individual vcpu structs */
> if (!(vcpu = virDomainDefGetVcpu(dom->def, cpuinfo[i].number)))
> continue;
>
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