Messages in this thread | | | Date | Tue, 25 Feb 2020 15:50:28 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH v2 4/5] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU |
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Gautham R Shenoy wrote: > On Fri, Feb 21, 2020 at 10:50:12AM -0600, Nathan Lynch wrote: >> "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes: >> > diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c >> > index 80a676d..5b4b450 100644 >> > --- a/arch/powerpc/kernel/sysfs.c >> > +++ b/arch/powerpc/kernel/sysfs.c >> > @@ -19,6 +19,7 @@ >> > #include <asm/smp.h> >> > #include <asm/pmc.h> >> > #include <asm/firmware.h> >> > +#include <asm/idle.h> >> > #include <asm/svm.h> >> > >> > #include "cacheinfo.h" >> > @@ -733,6 +734,42 @@ static void create_svm_file(void) >> > } >> > #endif /* CONFIG_PPC_SVM */ >> > >> > +static void read_idle_purr(void *val) >> > +{ >> > + u64 *ret = (u64 *)val; >> >> No cast from void* needed. > > Will fix this. Thanks. > >> >> >> > + >> > + *ret = read_this_idle_purr(); >> > +} >> > + >> > +static ssize_t idle_purr_show(struct device *dev, >> > + struct device_attribute *attr, char *buf) >> > +{ >> > + struct cpu *cpu = container_of(dev, struct cpu, dev); >> > + u64 val; >> > + >> > + smp_call_function_single(cpu->dev.id, read_idle_purr, &val, 1); >> > + return sprintf(buf, "%llx\n", val); >> > +} >> > +static DEVICE_ATTR(idle_purr, 0400, idle_purr_show, NULL); >> > + >> > +static void read_idle_spurr(void *val) >> > +{ >> > + u64 *ret = (u64 *)val; >> > + >> > + *ret = read_this_idle_spurr(); >> > +} >> > + >> > +static ssize_t idle_spurr_show(struct device *dev, >> > + struct device_attribute *attr, char *buf) >> > +{ >> > + struct cpu *cpu = container_of(dev, struct cpu, dev); >> > + u64 val; >> > + >> > + smp_call_function_single(cpu->dev.id, read_idle_spurr, &val, 1); >> > + return sprintf(buf, "%llx\n", val); >> > +} >> > +static DEVICE_ATTR(idle_spurr, 0400, idle_spurr_show, NULL); >> >> It's regrettable that we have to wake up potentially idle CPUs in order >> to derive correct idle statistics for them, but I suppose the main user >> (lparstat) of these interfaces already is causing this to happen by >> polling the existing per-cpu purr and spurr attributes. >> >> So now lparstat will incur at minimum four syscalls and four IPIs per >> CPU per polling interval -- one for each of purr, spurr, idle_purr and >> idle_spurr. Correct? > > Yes, it is unforunate that we will end up making four syscalls and > generating IPI noise, and this is something that I discussed with > Naveen and Kamalesh. We have the following two constraints: > > 1) These values of PURR and SPURR required are per-cpu. Hence putting > them in lparcfg is not an option. > > 2) sysfs semantics encourages a single value per key, the key being > the sysfs-file. Something like the following would have made far more > sense. > > cat /sys/devices/system/cpu/cpuX/purr_spurr_accounting > purr:A > idle_purr:B > spurr:C > idle_spurr:D > > There are some sysfs files which allow something like this. Eg: > /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state > > Thoughts on any other alternatives?
Umm... procfs? /me ducks
> > >> >> At some point it's going to make sense to batch sampling of remote CPUs' >> SPRs.
How did you mean this? It looks like we first need to provide a separate user interface, since with the existing sysfs interface providing separate files, I am not sure if we can batch such reads.
- Naveen
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