On Fri, Sep 13, 2024 at 12:17 PM Mattias Rönnblom <hof...@lysator.liu.se> wrote:
>
> On 2024-09-12 17:11, Jerin Jacob wrote:
> > On Thu, Sep 12, 2024 at 6:50 PM Mattias Rönnblom <hof...@lysator.liu.se>
> > wrote:
> >>
> >> On 2024-09-12 15:09, Jerin Jacob wrote:
> >>> On Thu, Sep 12, 2024 at 2:34 PM Mattias Rönnblom
> >>> <mattias.ronnb...@ericsson.com> wrote:
> >>>>
> >>>> Add basic micro benchmark for lcore variables, in an attempt to assure
> >>>> that the overhead isn't significantly greater than alternative
> >>>> approaches, in scenarios where the benefits aren't expected to show up
> >>>> (i.e., when plenty of cache is available compared to the working set
> >>>> size of the per-lcore data).
> >>>>
> >>>> Signed-off-by: Mattias Rönnblom <mattias.ronnb...@ericsson.com>
> >>>> ---
> >>>> app/test/meson.build | 1 +
> >>>> app/test/test_lcore_var_perf.c | 160 +++++++++++++++++++++++++++++++++
> >>>> 2 files changed, 161 insertions(+)
> >>>> create mode 100644 app/test/test_lcore_var_perf.c
> >>>
> >>>
> >>>> +static double
> >>>> +benchmark_access_method(void (*init_fun)(void), void
> >>>> (*update_fun)(void))
> >>>> +{
> >>>> + uint64_t i;
> >>>> + uint64_t start;
> >>>> + uint64_t end;
> >>>> + double latency;
> >>>> +
> >>>> + init_fun();
> >>>> +
> >>>> + start = rte_get_timer_cycles();
> >>>> +
> >>>> + for (i = 0; i < ITERATIONS; i++)
> >>>> + update_fun();
> >>>> +
> >>>> + end = rte_get_timer_cycles();
> >>>
> >>> Use precise variant. rte_rdtsc_precise() or so to be accurate
> >>
> >> With 1e7 iterations, do you need rte_rdtsc_precise()? I suspect not.
> >
> > I was thinking in another way, with 1e7 iteration, the additional
> > barrier on precise will be amortized, and we get more _deterministic_
> > behavior e.s.p in case if we print cycles and if we need to catch
> > regressions.
>
> If you time a section of code which spends ~40000000 cycles, it doesn't
> matter if you add or remove a few cycles at the beginning and the end.
>
> The rte_rdtsc_precise() is both better (more precise in the sense of
> more serialization), and worse (because it's more costly, and thus more
> intrusive).
We can calibrate the overhead to remove the cost.
>
> You can use rte_rdtsc_precise(), rte_rdtsc(), or gettimeofday(). It
> doesn't matter.
Yes. In this setup and it is pretty inaccurate PER iteration. Please
refer to the below patch to see the difference.
Patch 1: Make nanoseconds to cycles per iteration
------------------------------------------------------------------
diff --git a/app/test/test_lcore_var_perf.c b/app/test/test_lcore_var_perf.c
index ea1d7ba90b52..b8d25400f593 100644
--- a/app/test/test_lcore_var_perf.c
+++ b/app/test/test_lcore_var_perf.c
@@ -110,7 +110,7 @@ benchmark_access_method(void (*init_fun)(void),
void (*update_fun)(void))
end = rte_get_timer_cycles();
- latency = ((end - start) / (double)rte_get_timer_hz()) / ITERATIONS;
+ latency = ((end - start)) / ITERATIONS;
return latency;
}
@@ -137,8 +137,7 @@ test_lcore_var_access(void)
- printf("Latencies [ns/update]\n");
+ printf("Latencies [cycles/update]\n");
printf("Thread-local storage Static array Lcore variables\n");
- printf("%20.1f %13.1f %16.1f\n", tls_latency * 1e9,
- sarray_latency * 1e9, lvar_latency * 1e9);
+ printf("%20.1f %13.1f %16.1f\n", tls_latency, sarray_latency,
lvar_latency);
return TEST_SUCCESS;
}
Patch 2: Change to precise with calibration
-----------------------------------------------------------
diff --git a/app/test/test_lcore_var_perf.c b/app/test/test_lcore_var_perf.c
index ea1d7ba90b52..8142ecd56241 100644
--- a/app/test/test_lcore_var_perf.c
+++ b/app/test/test_lcore_var_perf.c
@@ -96,23 +96,28 @@ lvar_update(void)
static double
benchmark_access_method(void (*init_fun)(void), void (*update_fun)(void))
{
- uint64_t i;
+ double tsc_latency;
+ double latency;
uint64_t start;
uint64_t end;
- double latency;
+ uint64_t i;
- init_fun();
+ /* calculate rte_rdtsc_precise overhead */
+ start = rte_rdtsc_precise();
+ end = rte_rdtsc_precise();
+ tsc_latency = (end - start);
- start = rte_get_timer_cycles();
+ init_fun();
- for (i = 0; i < ITERATIONS; i++)
+ latency = 0;
+ for (i = 0; i < ITERATIONS; i++) {
+ start = rte_rdtsc_precise();
update_fun();
+ end = rte_rdtsc_precise();
+ latency += (end - start) - tsc_latency;
+ }
- end = rte_get_timer_cycles();
-
- latency = ((end - start) / (double)rte_get_timer_hz()) / ITERATIONS;
-
- return latency;
+ return latency / (double)ITERATIONS;
}
static int
@@ -135,10 +140,9 @@ test_lcore_var_access(void)
sarray_latency = benchmark_access_method(sarray_init, sarray_update);
lvar_latency = benchmark_access_method(lvar_init, lvar_update);
- printf("Latencies [ns/update]\n");
+ printf("Latencies [cycles/update]\n");
printf("Thread-local storage Static array Lcore variables\n");
- printf("%20.1f %13.1f %16.1f\n", tls_latency * 1e9,
- sarray_latency * 1e9, lvar_latency * 1e9);
+ printf("%20.1f %13.1f %16.1f\n", tls_latency, sarray_latency,
lvar_latency);
return TEST_SUCCESS;
}
ARM N2 core with patch 1(aka current scheme)
-----------------------------------
+ ------------------------------------------------------- +
+ Test Suite : lcore variable perf autotest
+ ------------------------------------------------------- +
Latencies [cycles/update]
Thread-local storage Static array Lcore variables
7.0 7.0 7.0
ARM N2 core with patch 2
-----------------------------------
+ ------------------------------------------------------- +
+ Test Suite : lcore variable perf autotest
+ ------------------------------------------------------- +
Latencies [cycles/update]
Thread-local storage Static array Lcore variables
11.4 15.5 15.5
x86 i9 core with patch 1(aka current scheme)
------------------------------------------------------------
+ ------------------------------------------------------- +
+ Test Suite : lcore variable perf autotest
+ ------------------------------------------------------- +
Latencies [ns/update]
Thread-local storage Static array Lcore variables
5.0 6.0 6.0
x86 i9 core with patch 2
--------------------------------
+ ------------------------------------------------------- +
+ Test Suite : lcore variable perf autotest
+ ------------------------------------------------------- +
Latencies [cycles/update]
Thread-local storage Static array Lcore variables
5.3 10.6 11.7
>
> > Furthermore, you may consider replacing rte_random() in fast path to
> > running number or so if it is not deterministic in cycle computation.
>
> rte_rand() is not used in the fast path. I don't understand what you
I missed that. Ignore this comment.
> mean by "running number".
