| Message ID | 1582262314-8319-4-git-send-email-ego@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Track and expose idle PURR and SPURR ticks | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/apply_patch | success | Successfully applied on branch powerpc/merge (65b2623f395a4e25ab3ff4cff1c9c7623619a22d) |
| snowpatch_ozlabs/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 75 lines checked |
| snowpatch_ozlabs/needsstable | success | Patch has no Fixes tags |
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes: > +static inline void snapshot_spurr_idle_entry(void) > +{ > + *this_cpu_ptr(&idle_entry_spurr_snap) = mfspr(SPRN_SPURR); > +} > + [...] > +static inline void update_idle_spurr_accounting(void) > +{ > + u64 *idle_spurr_cycles_ptr = this_cpu_ptr(&idle_spurr_cycles); > + u64 in_spurr = *this_cpu_ptr(&idle_entry_spurr_snap); > + > + *idle_spurr_cycles_ptr += mfspr(SPRN_SPURR) - in_spurr; > +} [...] > +static inline u64 read_this_idle_spurr(void) > +{ > + /* > + * If we are reading from an idle context, update the > + * idle-spurr cycles corresponding to the last idle period. > + * Since the idle context is not yet over, take a fresh > + * snapshot of the idle-spurr. > + */ > + if (get_lppaca()->idle == 1) { > + update_idle_spurr_accounting(); > + snapshot_spurr_idle_entry(); This samples spurr twice when it could do with just one. I don't know the performance implications, but will the results be coherent?
Hello Nathan, On Fri, Feb 21, 2020 at 10:47:41AM -0600, Nathan Lynch wrote: > "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes: > > +static inline void snapshot_spurr_idle_entry(void) > > +{ > > + *this_cpu_ptr(&idle_entry_spurr_snap) = mfspr(SPRN_SPURR); > > +} > > + > > [...] > > > +static inline void update_idle_spurr_accounting(void) > > +{ > > + u64 *idle_spurr_cycles_ptr = this_cpu_ptr(&idle_spurr_cycles); > > + u64 in_spurr = *this_cpu_ptr(&idle_entry_spurr_snap); > > + > > + *idle_spurr_cycles_ptr += mfspr(SPRN_SPURR) - in_spurr; > > +} > > [...] > > > +static inline u64 read_this_idle_spurr(void) > > +{ > > + /* > > + * If we are reading from an idle context, update the > > + * idle-spurr cycles corresponding to the last idle period. > > + * Since the idle context is not yet over, take a fresh > > + * snapshot of the idle-spurr. > > + */ > > + if (get_lppaca()->idle == 1) { > > + update_idle_spurr_accounting(); > > + snapshot_spurr_idle_entry(); > > This samples spurr twice when it could do with just one. I don't know > the performance implications, but will the results be coherent? We would have taken the snapshot in idle_loop_prolog() just before entering idle. That fact that the "if" condition is true above in read_this_idle_spurr() implies that we are reading the idle_spurr value from an interrupt context and since get_lppaca()->idle == 1, we haven't yet called idle_loop_epilog(), where we would have updated the idle_spurr ticks for the last idle period. Hence, in this function, we first update the idle_spurr accounting from the time of the last snapshot to now. We update the snapshot to the current SPURR value so that when we eventually call idle_loop_epilog(), we will account for the remaining idle duration, i.e from the read_this_idle_spurr() call to idle_loop_epilog() The results are therefore coherant, in that we do not perform double accounting the second time we invoke update_idle_spurr_accounting() from idle_loop_epilog(), but only add the spurr ticks from read_this_idle_spurr() to idle_loop_epilog(). -- Thanks and Regards gautham.
diff --git a/arch/powerpc/include/asm/idle.h b/arch/powerpc/include/asm/idle.h index 126a217..db82fc1 100644 --- a/arch/powerpc/include/asm/idle.h +++ b/arch/powerpc/include/asm/idle.h @@ -2,13 +2,20 @@ #define _ASM_POWERPC_IDLE_H #include <asm/runlatch.h> +DECLARE_PER_CPU(u64, idle_spurr_cycles); DECLARE_PER_CPU(u64, idle_entry_purr_snap); +DECLARE_PER_CPU(u64, idle_entry_spurr_snap); static inline void snapshot_purr_idle_entry(void) { *this_cpu_ptr(&idle_entry_purr_snap) = mfspr(SPRN_PURR); } +static inline void snapshot_spurr_idle_entry(void) +{ + *this_cpu_ptr(&idle_entry_spurr_snap) = mfspr(SPRN_SPURR); +} + static inline void update_idle_purr_accounting(void) { u64 wait_cycles; @@ -19,10 +26,19 @@ static inline void update_idle_purr_accounting(void) get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles); } +static inline void update_idle_spurr_accounting(void) +{ + u64 *idle_spurr_cycles_ptr = this_cpu_ptr(&idle_spurr_cycles); + u64 in_spurr = *this_cpu_ptr(&idle_entry_spurr_snap); + + *idle_spurr_cycles_ptr += mfspr(SPRN_SPURR) - in_spurr; +} + static inline void idle_loop_prolog(void) { ppc64_runlatch_off(); snapshot_purr_idle_entry(); + snapshot_spurr_idle_entry(); /* * Indicate to the HV that we are idle. Now would be * a good time to find other work to dispatch. @@ -33,6 +49,7 @@ static inline void idle_loop_prolog(void) static inline void idle_loop_epilog(void) { update_idle_purr_accounting(); + update_idle_spurr_accounting(); get_lppaca()->idle = 0; ppc64_runlatch_on(); } @@ -52,4 +69,20 @@ static inline u64 read_this_idle_purr(void) return be64_to_cpu(get_lppaca()->wait_state_cycles); } + +static inline u64 read_this_idle_spurr(void) +{ + /* + * If we are reading from an idle context, update the + * idle-spurr cycles corresponding to the last idle period. + * Since the idle context is not yet over, take a fresh + * snapshot of the idle-spurr. + */ + if (get_lppaca()->idle == 1) { + update_idle_spurr_accounting(); + snapshot_spurr_idle_entry(); + } + + return *this_cpu_ptr(&idle_spurr_cycles); +} #endif diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c index e9f2cefa..5ef5c82 100644 --- a/arch/powerpc/platforms/pseries/setup.c +++ b/arch/powerpc/platforms/pseries/setup.c @@ -318,7 +318,9 @@ static int alloc_dispatch_log_kmem_cache(void) } machine_early_initcall(pseries, alloc_dispatch_log_kmem_cache); +DEFINE_PER_CPU(u64, idle_spurr_cycles); DEFINE_PER_CPU(u64, idle_entry_purr_snap); +DEFINE_PER_CPU(u64, idle_entry_spurr_snap); static void pseries_lpar_idle(void) { /*