Re: [PATCH v2 1/2] app/test: add cksum performance test

[Olivier Matz <olivier.matz@6wind.com>]

On Mon, Jul 11, 2022 at 10:42:37AM +0000, Mattias Rönnblom wrote:
> On 2022-07-11 11:47, Olivier Matz wrote:
> > Hi Mattias,
> > 
> > Please see few comments below.
> > 
> > On Fri, Jul 08, 2022 at 02:56:07PM +0200, Mattias Rönnblom wrote:
> >> Add performance test for the rte_raw_cksum() function, which delegates
> >> the actual work to __rte_raw_cksum(), which in turn is used by other
> >> functions in need of Internet checksum calculation.
> >>
> >> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> >>
> >> ---
> >>
> >> v2:
> >>    * Added __rte_unused to unused volatile variable, to keep the Intel
> >>      compiler happy.
> >> ---
> >>   MAINTAINERS                |   1 +
> >>   app/test/meson.build       |   1 +
> >>   app/test/test_cksum_perf.c | 118 +++++++++++++++++++++++++++++++++++++
> >>   3 files changed, 120 insertions(+)
> >>   create mode 100644 app/test/test_cksum_perf.c
> >>
> >> diff --git a/MAINTAINERS b/MAINTAINERS
> >> index c923712946..2a4c99e05a 100644
> >> --- a/MAINTAINERS
> >> +++ b/MAINTAINERS
> >> @@ -1414,6 +1414,7 @@ Network headers
> >>   M: Olivier Matz <olivier.matz@6wind.com>
> >>   F: lib/net/
> >>   F: app/test/test_cksum.c
> >> +F: app/test/test_cksum_perf.c
> >>   
> >>   Packet CRC
> >>   M: Jasvinder Singh <jasvinder.singh@intel.com>
> >> diff --git a/app/test/meson.build b/app/test/meson.build
> >> index 431c5bd318..191db03d1d 100644
> >> --- a/app/test/meson.build
> >> +++ b/app/test/meson.build
> >> @@ -18,6 +18,7 @@ test_sources = files(
> >>           'test_bpf.c',
> >>           'test_byteorder.c',
> >>           'test_cksum.c',
> >> +        'test_cksum_perf.c',
> >>           'test_cmdline.c',
> >>           'test_cmdline_cirbuf.c',
> >>           'test_cmdline_etheraddr.c',
> >> diff --git a/app/test/test_cksum_perf.c b/app/test/test_cksum_perf.c
> >> new file mode 100644
> >> index 0000000000..bff73cb3bb
> >> --- /dev/null
> >> +++ b/app/test/test_cksum_perf.c
> >> @@ -0,0 +1,118 @@
> >> +/* SPDX-License-Identifier: BSD-3-Clause
> >> + * Copyright(c) 2022 Ericsson AB
> >> + */
> >> +
> >> +#include <stdio.h>
> >> +
> >> +#include <rte_common.h>
> >> +#include <rte_cycles.h>
> >> +#include <rte_ip.h>
> >> +#include <rte_malloc.h>
> >> +#include <rte_random.h>
> >> +
> >> +#include "test.h"
> >> +
> >> +#define NUM_BLOCKS (10)
> >> +#define ITERATIONS (1000000)
> > 
> > Parenthesis can be safely removed
> > 
> >> +
> >> +static const size_t data_sizes[] = { 20, 21, 100, 101, 1500, 1501 };
> >> +
> >> +static __rte_noinline uint16_t
> >> +do_rte_raw_cksum(const void *buf, size_t len)
> >> +{
> >> +	return rte_raw_cksum(buf, len);
> >> +}
> > 
> > I don't understand the need to have this wrapper, especially marked
> > __rte_noinline. What is the objective?
> > 
> 
> The intention is to disallow the compiler to perform unrolling and 
> integrating/interleave one cksum operating with the next buffer's in a 
> way that wouldn't be feasable in a real application.
> 
> It will result in an overestimation of the cost for small cksums, so 
> it's still misleading, but in another direction. :)

OK, got it. I think it's fine like you did then.

> 
> > Note that when I remove the __rte_noinline, the performance is better
> > for size 20 and 21.
> > 
> >> +
> >> +static void
> >> +init_block(void *buf, size_t len)
> > 
> > Can buf be a (char *) instead?
> > It would avoid a cast below.
> > 
> 
> Yes.
> 
> >> +{
> >> +	size_t i;
> >> +
> >> +	for (i = 0; i < len; i++)
> >> +		((char *)buf)[i] = (uint8_t)rte_rand();
> >> +}
> >> +
> >> +static int
> >> +test_cksum_perf_size_alignment(size_t block_size, bool aligned)
> >> +{
> >> +	char *data[NUM_BLOCKS];
> >> +	char *blocks[NUM_BLOCKS];
> >> +	unsigned int i;
> >> +	uint64_t start;
> >> +	uint64_t end;
> >> +	/* Floating point to handle low (pseudo-)TSC frequencies */
> >> +	double block_latency;
> >> +	double byte_latency;
> >> +	volatile __rte_unused uint64_t sum = 0;
> >> +
> >> +	for (i = 0; i < NUM_BLOCKS; i++) {
> >> +		data[i] = rte_malloc(NULL, block_size + 1, 0);
> >> +
> >> +		if (data[i] == NULL) {
> >> +			printf("Failed to allocate memory for block\n");
> >> +			return TEST_FAILED;
> >> +		}
> >> +
> >> +		init_block(data[i], block_size + 1);
> >> +
> >> +		blocks[i] = aligned ? data[i] : data[i] + 1;
> >> +	}
> >> +
> >> +	start = rte_rdtsc();
> >> +
> >> +	for (i = 0; i < ITERATIONS; i++) {
> >> +		unsigned int j;
> >> +		for (j = 0; j < NUM_BLOCKS; j++)
> >> +			sum += do_rte_raw_cksum(blocks[j], block_size);
> >> +	}
> >> +
> >> +	end = rte_rdtsc();
> >> +
> >> +	block_latency = (end - start) / (double)(ITERATIONS * NUM_BLOCKS);
> >> +	byte_latency = block_latency / block_size;
> >> +
> >> +	printf("%-9s %10zd %19.1f %16.2f\n", aligned ? "Aligned" : "Unaligned",
> >> +	       block_size, block_latency, byte_latency);
> > 
> > When I run the test on my dev machine, I get the following results,
> > which are quite reproductible:
> > 
> > Aligned           20       10.4      0.52     (range is 0.48 - 0.52)
> > Unaligned         20        7.9      0.39     (range is 0.39 - 0.40)
> > ...
> > 
> > If I increase the number of iterations, the first results
> > change significantly:
> > 
> > Aligned           20        8.2      0.42     (range is 0.41 - 0.42)
> > Unaligned         20        8.0      0.40     (always this value)
> 
> 
> I suspect you have frequency scaling enabled on your system. This is 
> generally not advisable, you want to some level of determinism in when 
> benchmarking. Especially on short runs like this is (and must be).
> 
> I thought about doing something about this, but it seemed like an issue 
> that should be addressed on a framework level, rather than on a per-perf 
> autotest level.
> 
> If you want your CPU core to scale up, you can just insert
> 
> rte_delay_block_us(100000);
> 
> before the actual test is run.

Your hypothesis is correct. When I disable frequency scaling, the results
are now the same with 100K, 1M or 10M iterations.

However, adding a rte_delay_us_block() does not really solve the issue,
probably because it calls rte_pause() in the loop.

> Should I add this? I *think* 100 ms should be enough, but maybe someone 
> with more in-depth knowledge of the frequency governors can comment on this.

Anyway, I think we don't need to add the blocking delay, we can
legitimally expect that freq scaling is disabled when we run performance
tests.

> 
> > 
> > To have more precise tests with small size, would it make sense to
> > target a test time instead of an iteration count? Something like
> > this:
> > 
> 
> The time lost when running on a lower frequency (plus the hiccups when 
> the frequency is changed) will be amortized as you add to the length of 
> the test run, which will partly solved the problem. A better solution is 
> to not start the test before the core runs on the max frequency.
> 
> Again, this is assuming DVFS is what you suffer from here. I guess in 
> theory it could be TLB miss as well.
> 
> > 	#define ITERATIONS 1000000
> > 	uint64_t iterations = 0;
> > 
> > 	...
> > 
> > 	do {
> > 		for (i = 0; i < ITERATIONS; i++) {
> > 			unsigned int j;
> > 			for (j = 0; j < NUM_BLOCKS; j++)
> > 				sum += do_rte_raw_cksum(blocks[j], block_size);
> > 		}
> > 		iterations += ITERATIONS;
> > 		end = rte_rdtsc();
> > 	} while ((end - start) < rte_get_tsc_hz());
> > 
> > 	block_latency = (end - start) / (double)(iterations * NUM_BLOCKS);
> > 
> > 
> > After this change, the aligned and unaligned cases have the same
> > performance on my machine.
> > 
> > 
> 
> RTE>>cksum_perf_autotest
> ### rte_raw_cksum() performance ###
> Alignment  Block size    TSC cycles/block  TSC cycles/byte
> Aligned           20                16.1             0.81
> Unaligned         20                16.1             0.81
> 
> ... with the 100 ms busy-wait delay (and frequency scaling enabled) on 
> my AMD machine.
> 
> >> +
> >> +	for (i = 0; i < NUM_BLOCKS; i++)
> >> +		rte_free(data[i]);
> >> +
> >> +	return TEST_SUCCESS;
> >> +}
> >> +
> >> +static int
> >> +test_cksum_perf_size(size_t block_size)
> >> +{
> >> +	int rc;
> >> +
> >> +	rc = test_cksum_perf_size_alignment(block_size, true);
> >> +	if (rc != TEST_SUCCESS)
> >> +		return rc;
> >> +
> >> +	rc = test_cksum_perf_size_alignment(block_size, false);
> >> +
> >> +	return rc;
> >> +}
> >> +
> >> +static int
> >> +test_cksum_perf(void)
> >> +{
> >> +	uint16_t i;
> >> +
> >> +	printf("### rte_raw_cksum() performance ###\n");
> >> +	printf("Alignment  Block size    TSC cycles/block  TSC cycles/byte\n");
> >> +
> >> +	for (i = 0; i < RTE_DIM(data_sizes); i++) {
> >> +		int rc;
> >> +
> >> +		rc = test_cksum_perf_size(data_sizes[i]);
> >> +		if (rc != TEST_SUCCESS)
> >> +			return rc;
> >> +	}
> >> +
> >> +	return TEST_SUCCESS;
> >> +}
> >> +
> >> +
> >> +REGISTER_TEST_COMMAND(cksum_perf_autotest, test_cksum_perf);
> >> +
> > 
> > The last empty line can be removed.
> > 
> 
> OK.
> 
> Thanks for the review. I will send a v3 as soon as we've settled the 
> DVFS issue.
> 
> >> -- 
> >> 2.25.1
> >>
>