Date:   Wed, 3 Mar 2021 13:02:32 +0530
From:   Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     Thomas Richter <tmricht@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org, svens@...ux.ibm.com, gor@...ux.ibm.com,
        sumanthk@...ux.ibm.com, heiko.carstens@...ibm.com
Subject: Re: [PATCH] perf test: Test case 27 fails on s390 and non-x86
 platforms



> On 03-Mar-2021, at 1:40 AM, Liang, Kan <kan.liang@...ux.intel.com> wrote:
> 
> 
> 
> On 3/2/2021 12:08 PM, Thomas Richter wrote:
>> On 3/2/21 4:23 PM, Liang, Kan wrote:
>>> 
>>> 
>>> On 3/2/2021 9:48 AM, Thomas Richter wrote:
>>>> On 3/2/21 3:03 PM, Liang, Kan wrote:
>>>>> 
>>>>> + Athira Rajeev
>>>>> 
>>>>> On 3/2/2021 8:31 AM, Thomas Richter wrote:
>>>>>> Executing perf test 27 fails on s390:
>>>>>>    [root@...lp46 perf]# ./perf test -Fv 27
>>>>>>    27: Sample parsing
>>>>>>    --- start ---
>>>>>>    ---- end ----
>>>>>>    Sample parsing: FAILED!
>>>>>>    [root@...lp46 perf]#
>>>>>> 
>>>>>> The root cause is
>>>>>> commit c7444297fd3769 ("perf test: Support PERF_SAMPLE_WEIGHT_STRUCT")
>>>>>> This commit introduced a test case for PERF_SAMPLE_WEIGHT_STRUCT
>>>>>> but does not adjust non-x86 weak linkage functions.
>>>>>> 
>>>>>> The error is in test__sample_parsing() --> do_test()
>>>>>> Function do_test() defines two structures of type struct perf_sample named
>>>>>> sample and sample_out. The first sets member sample.ins_lat = 117
>>>>>> 
>>>>>> Structure sample_out is constructed dynamically using functions
>>>>>> perf_event__synthesize_sample() and evsel__parse_sample().
>>>>>> Both functions have an x86 specific function version which sets member
>>>>>> ins_lat. The weak common functions do not set member ins_lat.
>>>>>> 
>>>>> 
>>>>> I don't think Power supports the instruction latency. As a request from Athira Rajeev, I moved the PERF_SAMPLE_WEIGHT_STRUCT to the X86 specific codes.
>>>>> https://lore.kernel.org/lkml/D97FEF4F-DD88-4760-885E-9A6161A9B48B@linux.vnet.ibm.com/
>>>>> https://lore.kernel.org/lkml/1612540912-6562-1-git-send-email-kan.liang@linux.intel.com/
>>>>> 
>>>>> I don't think we want to add the ins_lat back in the weak common functions.


Hi Kan Liang,

Yes, presently in powerpc we are not using PERF_SAMPLE_WEIGHT_STRUCT.
But I am working on a patch set to expose some of the pipeline stalls details using PERF_SAMPLE_WEIGHT_STRUCT,
by using the two 16-bit fields of sample weight. I could use the same "ins_lat" field and then use an arch specific header string while displaying with "perf report”. I will be sharing an RFC patch on this soon.

But I believe it is good to keep the weak function "arch_perf_parse_sample_weight" if we want to create different field for 'weight->var2_w' in future.

Thanks
Athira

>>>>> 
>>>>> Could you please update the perf test and don't apply the PERF_SAMPLE_WEIGHT_STRUCT for the non-X86 platform?
>>>> 
>>>> I used offical linux git tree
>>>>   [root@...lp46 perf]# git tag | fgrep 5.12
>>>> v5.12-rc1
>>>> [root@...lp46 perf]#
>>>> 
>>>> So this change is in the pipe. I do not plan to revert individual patches.
>>> 
>>> No, we shouldn't revert the patch.
>>> I mean can you fix the issue in perf test?
>>> Don't test ins_lat or PERF_SAMPLE_WEIGHT_STRUCT for a non-X86 platform.
>> That would be very ugly code. We would end up in conditional compiles like
>> #ifdef __s390x__
>> #endif
>> and other architectes like ARM/POWER etc come along. This is something I want to avoid.
> 
> The ins_lat is a model specific variable. Maybe we should move it to the arch specific test.
> 
> 
>> And this fix only touches perf, not the kernel.
> 
> The patch changes the behavior of the PERF_SAMPLE_WEIGHT. The high 32 bit will be dropped. It should bring some problems if the high 32 bit contains valid information.
> 
>>>>> 
>>>>> 
>>>>>> Later in function samples_same() both data in variable sample and sample_out
>>>>>> are compared. The comparison fails because sample.ins_lat is 117
>>>>>> and samples_out.ins_lat is 0, the weak functions never set member ins_lat.
>>>>>> 
>>>>>> Output after:
>>>>>>    [root@...lp46 perf]# ./perf test -Fv 27
>>>>>>    27: Sample parsing
>>>>>>    --- start ---
>>>>>>    ---- end ----
>>>>>>    Sample parsing: Ok
>>>>>> [root@...lp46 perf]#
>>>>>> 
>>>>>> Fixes:
>>>>>> commit c7444297fd3769 ("perf test: Support PERF_SAMPLE_WEIGHT_STRUCT")
>>>>> 
>>>>> I think the regression should start from
>>>>> commit fbefe9c2f87f ("perf tools: Support arch specific PERF_SAMPLE_WEIGHT_STRUCT processing")
>>>>> 
>>>>> 
>>>>> Thanks,
>>>>> Kan
>>>> 
>>>> Kan,
>>>> 
>>>> I do not follow you. Your commit c7444297fd3769d10c7ffb52c81d71503b3e268f
>>>> adds this line
>>>> 
>>>> @@ -242,6 +245,7 @@ static int do_test(u64 sample_type, u64 sample_regs, u64 read_format)
>>>>                  .cgroup         = 114,
>>>>                  .data_page_size = 115,
>>>>                  .code_page_size = 116,
>>>> +               .ins_lat        = 117,
>>>> 
>>>> And this assignment 117 breaks the test. As mentioned before, member ins_lat is never touched
>>>> by the weak functions.
>>>> 
>>> 
>>> Here is the timeline for the patches.
>>> 
>>> 1. The commit c7444297fd3769 and other SPR patches are merged at 2021-02-08. At that time, I don't think we have this issue. perf test should work well.
>> Nope, that line above 'ins_lat = 117.' breaks the test. Comment it out and it works well!!!
> 
> If you revert the commit fbefe9c2f87f, perf test should work well too.
> 
> The root cause of the issue is that the commit fbefe9c2f87f change the ins_lat to a model-specific variable, but perf test still verify the variable in the generic test.
> 
> The below patch moves the PERF_SAMPLE_WEIGHT test into a X86 specific test.
> 
> Does it work for you?
> 
> ---
> tools/perf/arch/x86/include/arch-tests.h   |   1 +
> tools/perf/arch/x86/tests/Build            |   1 +
> tools/perf/arch/x86/tests/arch-tests.c     |   4 +
> tools/perf/arch/x86/tests/sample-parsing.c | 125 +++++++++++++++++++++++++++++
> tools/perf/tests/sample-parsing.c          |   4 -
> 5 files changed, 131 insertions(+), 4 deletions(-)
> create mode 100644 tools/perf/arch/x86/tests/sample-parsing.c
> 
> diff --git a/tools/perf/arch/x86/include/arch-tests.h b/tools/perf/arch/x86/include/arch-tests.h
> index 6a54b94..0e20f3d 100644
> --- a/tools/perf/arch/x86/include/arch-tests.h
> +++ b/tools/perf/arch/x86/include/arch-tests.h
> @@ -10,6 +10,7 @@ int test__rdpmc(struct test *test __maybe_unused, int subtest);
> int test__insn_x86(struct test *test __maybe_unused, int subtest);
> int test__intel_pt_pkt_decoder(struct test *test, int subtest);
> int test__bp_modify(struct test *test, int subtest);
> +int test__x86_sample_parsing(struct test *test, int subtest);
> 
> #ifdef HAVE_DWARF_UNWIND_SUPPORT
> struct thread;
> diff --git a/tools/perf/arch/x86/tests/Build b/tools/perf/arch/x86/tests/Build
> index 36d4f24..28d7933 100644
> --- a/tools/perf/arch/x86/tests/Build
> +++ b/tools/perf/arch/x86/tests/Build
> @@ -3,5 +3,6 @@ perf-$(CONFIG_DWARF_UNWIND) += dwarf-unwind.o
> 
> perf-y += arch-tests.o
> perf-y += rdpmc.o
> +perf-y += sample-parsing.o
> perf-$(CONFIG_AUXTRACE) += insn-x86.o intel-pt-pkt-decoder-test.o
> perf-$(CONFIG_X86_64) += bp-modify.o
> diff --git a/tools/perf/arch/x86/tests/arch-tests.c b/tools/perf/arch/x86/tests/arch-tests.c
> index bc25d72..71aa673 100644
> --- a/tools/perf/arch/x86/tests/arch-tests.c
> +++ b/tools/perf/arch/x86/tests/arch-tests.c
> @@ -31,6 +31,10 @@ struct test arch_tests[] = {
> 	},
> #endif
> 	{
> +		.desc = "x86 Sample parsing",
> +		.func = test__x86_sample_parsing,
> +	},
> +	{
> 		.func = NULL,
> 	},
> 
> diff --git a/tools/perf/arch/x86/tests/sample-parsing.c b/tools/perf/arch/x86/tests/sample-parsing.c
> new file mode 100644
> index 0000000..28bbc61
> --- /dev/null
> +++ b/tools/perf/arch/x86/tests/sample-parsing.c
> @@ -0,0 +1,125 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <stdbool.h>
> +#include <inttypes.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <linux/bitops.h>
> +#include <linux/kernel.h>
> +#include <linux/types.h>
> +
> +#include "map_symbol.h"
> +#include "branch.h"
> +#include "event.h"
> +#include "evsel.h"
> +#include "debug.h"
> +#include "util/synthetic-events.h"
> +
> +#include "tests/tests.h"
> +#include "arch-tests.h"
> +
> +#define COMP(m) do {					\
> +	if (s1->m != s2->m) {				\
> +		pr_debug("Samples differ at '"#m"'\n");	\
> +		return false;				\
> +	}						\
> +} while (0)
> +
> +static bool samples_same(const struct perf_sample *s1,
> +			 const struct perf_sample *s2,
> +			 u64 type)
> +{
> +	if (type & PERF_SAMPLE_WEIGHT_STRUCT)
> +		COMP(ins_lat);
> +
> +	return true;
> +}
> +
> +static int do_test(u64 sample_type, u64 read_format)
> +{
> +	struct evsel evsel = {
> +		.needs_swap = false,
> +		.core = {
> +			. attr = {
> +				.sample_type = sample_type,
> +				.read_format = read_format,
> +			},
> +		},
> +	};
> +	union perf_event *event;
> +	struct perf_sample sample = {
> +		.weight		= 101,
> +		.ins_lat        = 102,
> +	};
> +	struct perf_sample sample_out;
> +	size_t i, sz, bufsz;
> +	int err, ret = -1;
> +
> +	sz = perf_event__sample_event_size(&sample, sample_type, read_format);
> +	bufsz = sz + 4096; /* Add a bit for overrun checking */
> +	event = malloc(bufsz);
> +	if (!event) {
> +		pr_debug("malloc failed\n");
> +		return -1;
> +	}
> +
> +	memset(event, 0xff, bufsz);
> +	event->header.type = PERF_RECORD_SAMPLE;
> +	event->header.misc = 0;
> +	event->header.size = sz;
> +
> +	err = perf_event__synthesize_sample(event, sample_type, read_format,
> +					    &sample);
> +	if (err) {
> +		pr_debug("%s failed for sample_type %#"PRIx64", error %d\n",
> +			 "perf_event__synthesize_sample", sample_type, err);
> +		goto out_free;
> +	}
> +
> +	/* The data does not contain 0xff so we use that to check the size */
> +	for (i = bufsz; i > 0; i--) {
> +		if (*(i - 1 + (u8 *)event) != 0xff)
> +			break;
> +	}
> +	if (i != sz) {
> +		pr_debug("Event size mismatch: actual %zu vs expected %zu\n",
> +			 i, sz);
> +		goto out_free;
> +	}
> +
> +	evsel.sample_size = __evsel__sample_size(sample_type);
> +
> +	err = evsel__parse_sample(&evsel, event, &sample_out);
> +	if (err) {
> +		pr_debug("%s failed for sample_type %#"PRIx64", error %d\n",
> +			 "evsel__parse_sample", sample_type, err);
> +		goto out_free;
> +	}
> +
> +	if (!samples_same(&sample, &sample_out, sample_type)) {
> +		pr_debug("parsing failed for sample_type %#"PRIx64"\n",
> +			 sample_type);
> +		goto out_free;
> +	}
> +
> +	ret = 0;
> +out_free:
> +	free(event);
> +	if (ret && read_format)
> +		pr_debug("read_format %#"PRIx64"\n", read_format);
> +	return ret;
> +}
> +
> +/**
> + * test__x86_sample_parsing - test X86 specific sample parsing
> + *
> + * This function implements a test that synthesizes a sample event, parses it
> + * and then checks that the parsed sample matches the original sample.  The test
> + * checks sample format bits separately and together.  If the test passes %0 is
> + * returned, otherwise %-1 is returned.
> + *
> + * For now, PERF_SAMPLE_WEIGHT_STRUCT is the only X86 specific sample type.
> + */
> +int test__x86_sample_parsing(struct test *test __maybe_unused, int subtest __maybe_unused)
> +{
> +	return do_test(PERF_SAMPLE_WEIGHT_STRUCT, 0);
> +}
> diff --git a/tools/perf/tests/sample-parsing.c b/tools/perf/tests/sample-parsing.c
> index 0dbe3aa..8fd8a4e 100644
> --- a/tools/perf/tests/sample-parsing.c
> +++ b/tools/perf/tests/sample-parsing.c
> @@ -129,9 +129,6 @@ static bool samples_same(const struct perf_sample *s1,
> 	if (type & PERF_SAMPLE_WEIGHT)
> 		COMP(weight);
> 
> -	if (type & PERF_SAMPLE_WEIGHT_STRUCT)
> -		COMP(ins_lat);
> -
> 	if (type & PERF_SAMPLE_DATA_SRC)
> 		COMP(data_src);
> 
> @@ -245,7 +242,6 @@ static int do_test(u64 sample_type, u64 sample_regs, u64 read_format)
> 		.cgroup		= 114,
> 		.data_page_size = 115,
> 		.code_page_size = 116,
> -		.ins_lat        = 117,
> 		.aux_sample	= {
> 			.size	= sizeof(aux_data),
> 			.data	= (void *)aux_data,
> -- 
> 2.7.4
> 
> 
> Thanks,
> Kan

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