linux-kernel - Re: [PATCH V2 06/13] selftests/resctrl: Remove "once" parameter required to be false

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Message-ID: <774e04c0-c62a-48f3-bcef-a2300752bd16@intel.com>
Date: Mon, 30 Sep 2024 09:07:39 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC: <fenghua.yu@...el.com>, <shuah@...nel.org>, <tony.luck@...el.com>,
	<peternewman@...gle.com>, <babu.moger@....com>,
	Maciej Wieczór-Retman <maciej.wieczor-retman@...el.com>,
	<linux-kselftest@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 06/13] selftests/resctrl: Remove "once" parameter
 required to be false

Hi Ilpo,

On 9/30/24 6:49 AM, Ilpo Järvinen wrote:
> On Thu, 12 Sep 2024, Reinette Chatre wrote:
> 
>> The CMT, MBM, and MBA tests rely on a benchmark that runs while
>> the test makes changes to needed configuration (for example memory
>> bandwidth allocation) and takes needed measurements. By default
>> the "fill_buf" benchmark is used and by default (via its
>> "once = false" setting) "fill_buf" is configured to run until
>> terminated after the test completes.
>>
>> An unintended consequence of enabling the user to override the
>> benchmark also enables the user to change parameters to the
>> "fill_buf" benchmark. This enables the user to set "fill_buf" to
>> only cycle through the buffer once (by setting "once = true")
>> and thus breaking the CMT, MBA, and MBM tests that expect
>> workload/interference to be reflected by their measurements.
>>
>> Prevent user space from changing the "once" parameter and ensure
>> that it is always false for the CMT, MBA, and MBM tests.
>>
>> Suggested-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
>> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
>> ---
>> Changes since V1:
>> - New patch
>> ---
>>  tools/testing/selftests/resctrl/fill_buf.c      |  7 ++++---
>>  tools/testing/selftests/resctrl/resctrl.h       |  2 +-
>>  tools/testing/selftests/resctrl/resctrl_tests.c |  8 +++++++-
>>  tools/testing/selftests/resctrl/resctrl_val.c   | 11 +----------
>>  4 files changed, 13 insertions(+), 15 deletions(-)
>>
>> diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
>> index 34e5df721430..854f0108d8e6 100644
>> --- a/tools/testing/selftests/resctrl/fill_buf.c
>> +++ b/tools/testing/selftests/resctrl/fill_buf.c
>> @@ -151,7 +151,7 @@ unsigned char *alloc_buffer(size_t buf_size, int memflush)
>>  	return buf;
>>  }
>>  
>> -int run_fill_buf(size_t buf_size, int memflush, int op, bool once)
>> +int run_fill_buf(size_t buf_size, int memflush, int op)
>>  {
>>  	unsigned char *buf;
>>  
>> @@ -160,9 +160,10 @@ int run_fill_buf(size_t buf_size, int memflush, int op, bool once)
>>  		return -1;
>>  
>>  	if (op == 0)
>> -		fill_cache_read(buf, buf_size, once);
>> +		fill_cache_read(buf, buf_size, false);
>>  	else
>> -		fill_cache_write(buf, buf_size, once);
>> +		fill_cache_write(buf, buf_size, false);
>> +
>>  	free(buf);
>>  
>>  	return 0;
>> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
>> index 2dda56084588..51f5f4b25e06 100644
>> --- a/tools/testing/selftests/resctrl/resctrl.h
>> +++ b/tools/testing/selftests/resctrl/resctrl.h
>> @@ -142,7 +142,7 @@ int perf_event_open(struct perf_event_attr *hw_event, pid_t pid, int cpu,
>>  unsigned char *alloc_buffer(size_t buf_size, int memflush);
>>  void mem_flush(unsigned char *buf, size_t buf_size);
>>  void fill_cache_read(unsigned char *buf, size_t buf_size, bool once);
>> -int run_fill_buf(size_t buf_size, int memflush, int op, bool once);
>> +int run_fill_buf(size_t buf_size, int memflush, int op);
>>  int initialize_mem_bw_imc(void);
>>  int measure_mem_bw(const struct user_params *uparams,
>>  		   struct resctrl_val_param *param, pid_t bm_pid,
>> diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
>> index ecbb7605a981..bee4123a5a9b 100644
>> --- a/tools/testing/selftests/resctrl/resctrl_tests.c
>> +++ b/tools/testing/selftests/resctrl/resctrl_tests.c
>> @@ -266,7 +266,13 @@ int main(int argc, char **argv)
>>  		uparams.benchmark_cmd[1] = span_str;
>>  		uparams.benchmark_cmd[2] = "1";
>>  		uparams.benchmark_cmd[3] = "0";
>> -		uparams.benchmark_cmd[4] = "false";
>> +		/*
>> +		 * Fourth parameter was previously used to indicate
>> +		 * how long "fill_buf" should run for, with "false"
>> +		 * ("fill_buf" will keep running until terminated)
>> +		 * the only option that works.
>> +		 */
>> +		uparams.benchmark_cmd[4] = NULL;
>>  		uparams.benchmark_cmd[5] = NULL;
> 
> Why is the [5] assignment kept around? Is something depending on this 
> double NULL termination? This patch removed the access to [4] so I 
> don't see anything beyong [3] accessed explicitly.
> 

In this case this was kept to reduce changes in preparatory work since this will
all be replaced later with the more robust parameter handling. I'll remove
the [5] assignment.

Thank you.

Reinette