Re: [PATCH v4 1/1] qemu: add per-vcpu delay stats

On 2/19/21 9:08 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(a)selectel.ru&gt; > --- > 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) > +{ I know you took inspiration in existing code, but our standards have moved since that code was written, a bit. > + g_autofree char *proc = NULL; > + unsigned long long oncpu = 0; > + g_autofree FILE *schedstat = NULL; > + > + 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); I'd expect this to be an error. Except for the case when the file doesn't exist. > + } > + if (fscanf(schedstat, "%llu %llu", &oncpu, cpudelay) < 2) { > + virReportError(VIR_ERR_INTERNAL_ERROR, > + _("Unable to parse schedstat info at '%s'"), > + proc); And this has to be error always. > + } > + > + VIR_FORCE_FCLOSE(schedstat); > + return 0; I'm fixing this function a bit. > +} The rest looks okay. I'm pushing it. Reviewed-by: Michal Privoznik <mprivozn(a)redhat.com&gt; Congratulations on your first libvirt contribution! Michal Awesome, thank you!