| Message ID | 1479759895-10042-4-git-send-email-wei@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Wei, On 11/21/2016 03:24 PM, Wei Huang wrote: > From: Christopher Covington <cov@codeaurora.org> I really appreciate your work on these patches. If for any or all of these you have more lines added/modified than me (or using any other better metric), please make sure to change the author to be you with `git commit --amend --reset-author` or equivalent. > Calculate the numbers of cycles per instruction (CPI) implied by ARM > PMU cycle counter values. The code includes a strict checking facility > intended for the -icount option in TCG mode in the configuration file. > > Signed-off-by: Christopher Covington <cov@codeaurora.org> > Signed-off-by: Wei Huang <wei@redhat.com> > --- > arm/pmu.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++- > arm/unittests.cfg | 14 +++++++ > 2 files changed, 132 insertions(+), 1 deletion(-) > > diff --git a/arm/pmu.c b/arm/pmu.c > index 176b070..129ef1e 100644 > --- a/arm/pmu.c > +++ b/arm/pmu.c > @@ -104,6 +104,25 @@ static inline uint32_t id_dfr0_read(void) > asm volatile("mrc p15, 0, %0, c0, c1, 2" : "=r" (val)); > return val; > } > + > +/* > + * Extra instructions inserted by the compiler would be difficult to compensate > + * for, so hand assemble everything between, and including, the PMCR accesses > + * to start and stop counting. Total cycles = isb + mcr + 2*loop = 2 + 2*loop. > + */ > +static inline void precise_cycles_loop(int loop, uint32_t pmcr) Nit: I would call this precise_instrs_loop. How many cycles it takes is IMPLEMENTATION DEFINED. > +{ > + asm volatile( > + " mcr p15, 0, %[pmcr], c9, c12, 0\n" > + " isb\n" > + "1: subs %[loop], %[loop], #1\n" > + " bgt 1b\n" Is there any chance we might need an isb here, to prevent the stop from happening before or during the loop? Where ISBs are required, the Linux best practice is to diligently comment why they are needed. Perhaps it would be a good habit to carry over into kvm-unit-tests. > + " mcr p15, 0, %[z], c9, c12, 0\n" > + " isb\n" > + : [loop] "+r" (loop) > + : [pmcr] "r" (pmcr), [z] "r" (0) > + : "cc"); > +} > #elif defined(__aarch64__) > static inline uint32_t pmcr_read(void) > { > @@ -150,6 +169,25 @@ static inline uint32_t id_dfr0_read(void) > asm volatile("mrs %0, id_dfr0_el1" : "=r" (id)); > return id; > } > + > +/* > + * Extra instructions inserted by the compiler would be difficult to compensate > + * for, so hand assemble everything between, and including, the PMCR accesses > + * to start and stop counting. Total cycles = isb + msr + 2*loop = 2 + 2*loop. > + */ > +static inline void precise_cycles_loop(int loop, uint32_t pmcr) > +{ > + asm volatile( > + " msr pmcr_el0, %[pmcr]\n" > + " isb\n" > + "1: subs %[loop], %[loop], #1\n" > + " b.gt 1b\n" > + " msr pmcr_el0, xzr\n" > + " isb\n" > + : [loop] "+r" (loop) > + : [pmcr] "r" (pmcr) > + : "cc"); > +} > #endif > > /* > @@ -208,6 +246,79 @@ static bool check_cycles_increase(void) > return success; > } > > +/* > + * Execute a known number of guest instructions. Only odd instruction counts > + * greater than or equal to 3 are supported by the in-line assembly code. The Nit: needs updating as well (or removal if you prefer) > + * control register (PMCR_EL0) is initialized with the provided value (allowing > + * for example for the cycle counter or event counters to be reset). At the end > + * of the exact instruction loop, zero is written to PMCR_EL0 to disable > + * counting, allowing the cycle counter or event counters to be read at the > + * leisure of the calling code. > + */ > +static void measure_instrs(int num, uint32_t pmcr) > +{ > + int loop = (num - 2) / 2; > + > + assert(num >= 4 && ((num - 2) % 2 == 0)); > + precise_cycles_loop(loop, pmcr); > +} > + > +/* > + * Measure cycle counts for various known instruction counts. Ensure that the > + * cycle counter progresses (similar to check_cycles_increase() but with more > + * instructions and using reset and stop controls). If supplied a positive, > + * nonzero CPI parameter, also strictly check that every measurement matches > + * it. Strict CPI checking is used to test -icount mode. > + */ > +static bool check_cpi(int cpi) > +{ > + uint32_t pmcr = pmcr_read() | PMU_PMCR_LC | PMU_PMCR_C | PMU_PMCR_E; > + > + /* init before event access, this test only cares about cycle count */ > + pmcntenset_write(1 << PMU_CYCLE_IDX); > + pmccfiltr_write(0); /* count cycles in EL0, EL1, but not EL2 */ > + > + if (cpi > 0) > + printf("Checking for CPI=%d.\n", cpi); > + printf("instrs : cycles0 cycles1 ...\n"); > + > + for (unsigned int i = 4; i < 300; i += 32) { > + uint64_t avg, sum = 0; > + > + printf("%d :", i); > + for (int j = 0; j < NR_SAMPLES; j++) { > + uint64_t cycles; > + > + pmccntr_write(0); > + measure_instrs(i, pmcr); > + cycles = pmccntr_read(); > + printf(" %"PRId64"", cycles); > + > + if (!cycles) { > + printf("\ncycles not incrementing!\n"); > + return false; > + } else if (cpi > 0 && cycles != i * cpi) { > + printf("\nunexpected cycle count received!\n"); > + return false; > + } else if ((cycles >> 32) != 0) { > + /* The cycles taken by the loop above should > + * fit in 32 bits easily. We check the upper > + * 32 bits of the cycle counter to make sure > + * there is no supprise. */ > + printf("\ncycle count bigger than 32bit!\n"); > + return false; > + } > + > + sum += cycles; > + } > + avg = sum / NR_SAMPLES; > + printf(" sum=%"PRId64" avg=%"PRId64" avg_ipc=%"PRId64" " > + "avg_cpi=%"PRId64"\n", sum, avg, i / avg, avg / i); > + } > + > + return true; > +} > + > void pmu_init(void) > { > uint32_t dfr0; > @@ -218,13 +329,19 @@ void pmu_init(void) > printf("PMU version: %d\n", pmu_version); > } This is clearly the right feature register to check. Sorry to have gotten excited about an inferior method. Cov
On 11/21/2016 03:40 PM, Christopher Covington wrote: > Hi Wei, > > On 11/21/2016 03:24 PM, Wei Huang wrote: >> From: Christopher Covington <cov@codeaurora.org> > > I really appreciate your work on these patches. If for any or all of these > you have more lines added/modified than me (or using any other better > metric), please make sure to change the author to be you with > `git commit --amend --reset-author` or equivalent. Sure, I will if needed. Regarding your comments below, I will fix the patch series after Drew's comments, if any. > >> Calculate the numbers of cycles per instruction (CPI) implied by ARM >> PMU cycle counter values. The code includes a strict checking facility >> intended for the -icount option in TCG mode in the configuration file. >> >> Signed-off-by: Christopher Covington <cov@codeaurora.org> >> Signed-off-by: Wei Huang <wei@redhat.com> >> --- >> arm/pmu.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++- >> arm/unittests.cfg | 14 +++++++ >> 2 files changed, 132 insertions(+), 1 deletion(-) >> >> diff --git a/arm/pmu.c b/arm/pmu.c >> index 176b070..129ef1e 100644 >> --- a/arm/pmu.c >> +++ b/arm/pmu.c >> @@ -104,6 +104,25 @@ static inline uint32_t id_dfr0_read(void) >> asm volatile("mrc p15, 0, %0, c0, c1, 2" : "=r" (val)); >> return val; >> } >> + >> +/* >> + * Extra instructions inserted by the compiler would be difficult to compensate >> + * for, so hand assemble everything between, and including, the PMCR accesses >> + * to start and stop counting. Total cycles = isb + mcr + 2*loop = 2 + 2*loop. ^^^^^^^^^^^^ I will change the comment above to "Total instrs". >> + */ >> +static inline void precise_cycles_loop(int loop, uint32_t pmcr) > > Nit: I would call this precise_instrs_loop. How many cycles it takes is > IMPLEMENTATION DEFINED. You are right. The cycle indeed depends on the design. Will fix. > >> +{ >> + asm volatile( >> + " mcr p15, 0, %[pmcr], c9, c12, 0\n" >> + " isb\n" >> + "1: subs %[loop], %[loop], #1\n" >> + " bgt 1b\n" > > Is there any chance we might need an isb here, to prevent the stop from happening > before or during the loop? Where ISBs are required, the Linux best practice is to In theory, I think this can happen when mcr is executed before all loop instructions completed, causing pmccntr_read() to miss some cycles. But QEMU TCG mode doesn't support out-order-execution. So the test condition, "cpi > 0 && cycles != i * cpi", will never be TRUE. Because cpi==0 in KVM, this same test condition won't be TRUE under KVM mode either. > diligently comment why they are needed. Perhaps it would be a good habit to > carry over into kvm-unit-tests. Agreed. Most isb() instructions were added following CP15 writes (not all CP15 writes, but at limited locations). We tried to follow what Linux kernel does in perf_event.c. If you feel that any isb() place needs special comment, I will be more than happy to add it. <snip> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Nov 21, 2016 at 04:49:20PM -0600, Wei Huang wrote: > > > On 11/21/2016 03:40 PM, Christopher Covington wrote: > > Hi Wei, > > > > On 11/21/2016 03:24 PM, Wei Huang wrote: > >> From: Christopher Covington <cov@codeaurora.org> > > > > I really appreciate your work on these patches. If for any or all of these > > you have more lines added/modified than me (or using any other better > > metric), please make sure to change the author to be you with > > `git commit --amend --reset-author` or equivalent. > > Sure, I will if needed. Regarding your comments below, I will fix the > patch series after Drew's comments, if any. > > > > >> Calculate the numbers of cycles per instruction (CPI) implied by ARM > >> PMU cycle counter values. The code includes a strict checking facility > >> intended for the -icount option in TCG mode in the configuration file. > >> > >> Signed-off-by: Christopher Covington <cov@codeaurora.org> > >> Signed-off-by: Wei Huang <wei@redhat.com> > >> --- > >> arm/pmu.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++- > >> arm/unittests.cfg | 14 +++++++ > >> 2 files changed, 132 insertions(+), 1 deletion(-) > >> > >> diff --git a/arm/pmu.c b/arm/pmu.c > >> index 176b070..129ef1e 100644 > >> --- a/arm/pmu.c > >> +++ b/arm/pmu.c > >> @@ -104,6 +104,25 @@ static inline uint32_t id_dfr0_read(void) > >> asm volatile("mrc p15, 0, %0, c0, c1, 2" : "=r" (val)); > >> return val; > >> } > >> + > >> +/* > >> + * Extra instructions inserted by the compiler would be difficult to compensate > >> + * for, so hand assemble everything between, and including, the PMCR accesses > >> + * to start and stop counting. Total cycles = isb + mcr + 2*loop = 2 + 2*loop. > ^^^^^^^^^^^^ > I will change the comment above to "Total instrs". > > >> + */ > >> +static inline void precise_cycles_loop(int loop, uint32_t pmcr) > > > > Nit: I would call this precise_instrs_loop. How many cycles it takes is > > IMPLEMENTATION DEFINED. > > You are right. The cycle indeed depends on the design. Will fix. > > > > >> +{ > >> + asm volatile( > >> + " mcr p15, 0, %[pmcr], c9, c12, 0\n" > >> + " isb\n" > >> + "1: subs %[loop], %[loop], #1\n" > >> + " bgt 1b\n" > > > > Is there any chance we might need an isb here, to prevent the stop from happening > > before or during the loop? Where ISBs are required, the Linux best practice is to > > In theory, I think this can happen when mcr is executed before all loop > instructions completed, causing pmccntr_read() to miss some cycles. But > QEMU TCG mode doesn't support out-order-execution. So the test > condition, "cpi > 0 && cycles != i * cpi", will never be TRUE. Because > cpi==0 in KVM, this same test condition won't be TRUE under KVM mode either. > > > diligently comment why they are needed. Perhaps it would be a good habit to > > carry over into kvm-unit-tests. > > Agreed. Most isb() instructions were added following CP15 writes (not > all CP15 writes, but at limited locations). We tried to follow what > Linux kernel does in perf_event.c. If you feel that any isb() place > needs special comment, I will be more than happy to add it. > > <snip> No new comments from me. Thanks guys for catching the need to update the comments. drew -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arm/pmu.c b/arm/pmu.c index 176b070..129ef1e 100644 --- a/arm/pmu.c +++ b/arm/pmu.c @@ -104,6 +104,25 @@ static inline uint32_t id_dfr0_read(void) asm volatile("mrc p15, 0, %0, c0, c1, 2" : "=r" (val)); return val; } + +/* + * Extra instructions inserted by the compiler would be difficult to compensate + * for, so hand assemble everything between, and including, the PMCR accesses + * to start and stop counting. Total cycles = isb + mcr + 2*loop = 2 + 2*loop. + */ +static inline void precise_cycles_loop(int loop, uint32_t pmcr) +{ + asm volatile( + " mcr p15, 0, %[pmcr], c9, c12, 0\n" + " isb\n" + "1: subs %[loop], %[loop], #1\n" + " bgt 1b\n" + " mcr p15, 0, %[z], c9, c12, 0\n" + " isb\n" + : [loop] "+r" (loop) + : [pmcr] "r" (pmcr), [z] "r" (0) + : "cc"); +} #elif defined(__aarch64__) static inline uint32_t pmcr_read(void) { @@ -150,6 +169,25 @@ static inline uint32_t id_dfr0_read(void) asm volatile("mrs %0, id_dfr0_el1" : "=r" (id)); return id; } + +/* + * Extra instructions inserted by the compiler would be difficult to compensate + * for, so hand assemble everything between, and including, the PMCR accesses + * to start and stop counting. Total cycles = isb + msr + 2*loop = 2 + 2*loop. + */ +static inline void precise_cycles_loop(int loop, uint32_t pmcr) +{ + asm volatile( + " msr pmcr_el0, %[pmcr]\n" + " isb\n" + "1: subs %[loop], %[loop], #1\n" + " b.gt 1b\n" + " msr pmcr_el0, xzr\n" + " isb\n" + : [loop] "+r" (loop) + : [pmcr] "r" (pmcr) + : "cc"); +} #endif /* @@ -208,6 +246,79 @@ static bool check_cycles_increase(void) return success; } +/* + * Execute a known number of guest instructions. Only odd instruction counts + * greater than or equal to 3 are supported by the in-line assembly code. The + * control register (PMCR_EL0) is initialized with the provided value (allowing + * for example for the cycle counter or event counters to be reset). At the end + * of the exact instruction loop, zero is written to PMCR_EL0 to disable + * counting, allowing the cycle counter or event counters to be read at the + * leisure of the calling code. + */ +static void measure_instrs(int num, uint32_t pmcr) +{ + int loop = (num - 2) / 2; + + assert(num >= 4 && ((num - 2) % 2 == 0)); + precise_cycles_loop(loop, pmcr); +} + +/* + * Measure cycle counts for various known instruction counts. Ensure that the + * cycle counter progresses (similar to check_cycles_increase() but with more + * instructions and using reset and stop controls). If supplied a positive, + * nonzero CPI parameter, also strictly check that every measurement matches + * it. Strict CPI checking is used to test -icount mode. + */ +static bool check_cpi(int cpi) +{ + uint32_t pmcr = pmcr_read() | PMU_PMCR_LC | PMU_PMCR_C | PMU_PMCR_E; + + /* init before event access, this test only cares about cycle count */ + pmcntenset_write(1 << PMU_CYCLE_IDX); + pmccfiltr_write(0); /* count cycles in EL0, EL1, but not EL2 */ + + if (cpi > 0) + printf("Checking for CPI=%d.\n", cpi); + printf("instrs : cycles0 cycles1 ...\n"); + + for (unsigned int i = 4; i < 300; i += 32) { + uint64_t avg, sum = 0; + + printf("%d :", i); + for (int j = 0; j < NR_SAMPLES; j++) { + uint64_t cycles; + + pmccntr_write(0); + measure_instrs(i, pmcr); + cycles = pmccntr_read(); + printf(" %"PRId64"", cycles); + + if (!cycles) { + printf("\ncycles not incrementing!\n"); + return false; + } else if (cpi > 0 && cycles != i * cpi) { + printf("\nunexpected cycle count received!\n"); + return false; + } else if ((cycles >> 32) != 0) { + /* The cycles taken by the loop above should + * fit in 32 bits easily. We check the upper + * 32 bits of the cycle counter to make sure + * there is no supprise. */ + printf("\ncycle count bigger than 32bit!\n"); + return false; + } + + sum += cycles; + } + avg = sum / NR_SAMPLES; + printf(" sum=%"PRId64" avg=%"PRId64" avg_ipc=%"PRId64" " + "avg_cpi=%"PRId64"\n", sum, avg, i / avg, avg / i); + } + + return true; +} + void pmu_init(void) { uint32_t dfr0; @@ -218,13 +329,19 @@ void pmu_init(void) printf("PMU version: %d\n", pmu_version); } -int main(void) +int main(int argc, char *argv[]) { + int cpi = 0; + + if (argc > 1) + cpi = atol(argv[1]); + report_prefix_push("pmu"); pmu_init(); report("Control register", check_pmcr()); report("Monotonically increasing cycle count", check_cycles_increase()); + report("Cycle/instruction ratio", check_cpi(cpi)); return report_summary(); } diff --git a/arm/unittests.cfg b/arm/unittests.cfg index 816f494..044d97c 100644 --- a/arm/unittests.cfg +++ b/arm/unittests.cfg @@ -63,3 +63,17 @@ groups = pci [pmu] file = pmu.flat groups = pmu + +# Test PMU support (TCG) with -icount IPC=1 +[pmu-tcg-icount-1] +file = pmu.flat +extra_params = -icount 0 -append '1' +groups = pmu +accel = tcg + +# Test PMU support (TCG) with -icount IPC=256 +[pmu-tcg-icount-256] +file = pmu.flat +extra_params = -icount 8 -append '256' +groups = pmu +accel = tcg