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Subject: Re: [PATCH] perf mmap: Discard head in overwrite_rb_find_range
To:     Jiri Olsa <jolsa@redhat.com>
References: <1520336663-53466-1-git-send-email-xieyisheng1@huawei.com>
 <20180307102157.GC22848@krava>
CC:     <acme@redhat.com>, <mingo@redhat.com>, <peterz@infradead.org>,
        <namhyung@kernel.org>, <alexander.shishkin@linux.intel.com>,
        <linux-kernel@vger.kernel.org>,
        Kan Liang <kan.liang@linux.intel.com>
From:   Yisheng Xie <xieyisheng1@huawei.com>
Message-ID: <2c7d1fe9-aeca-653e-569d-3078375bf588@huawei.com>
Date:   Wed, 7 Mar 2018 19:01:40 +0800
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Hi jirka,

On 2018/3/7 18:21, Jiri Olsa wrote:
> On Tue, Mar 06, 2018 at 07:44:23PM +0800, Yisheng Xie wrote:
>> In overwrite mode, start will be set to head in perf_mmap__read_init.
>> Therefore, it is no need to set the start one more in
>> overwrite_rb_find_range and *start can be used as head instead of
>> passing head to overwrite_rb_find_range.
> 
> it conflicts a little with recent cleanup from Kan Liang,,
>   https://marc.info/?t=152035082800001&r=1&w=2
> 
> otherwise it looks ok to me
> 

I can send the next version based on Kan's patch after his patches are in the tree.

Thanks
Yisheng

> jirka
> 
>>
>> Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
>> ---
>>  tools/perf/util/mmap.c | 15 +++++++--------
>>  1 file changed, 7 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
>> index 91531a7..6751ac9 100644
>> --- a/tools/perf/util/mmap.c
>> +++ b/tools/perf/util/mmap.c
>> @@ -223,19 +223,18 @@ int perf_mmap__mmap(struct perf_mmap *map, struct mmap_params *mp, int fd)
>>  	return 0;
>>  }
>>  
>> -static int overwrite_rb_find_range(void *buf, int mask, u64 head, u64 *start, u64 *end)
>> +static int overwrite_rb_find_range(void *buf, int mask, u64 *start, u64 *end)
>>  {
>>  	struct perf_event_header *pheader;
>> -	u64 evt_head = head;
>> +	u64 evt_head = *start;
>>  	int size = mask + 1;
>>  
>> -	pr_debug2("overwrite_rb_find_range: buf=%p, head=%"PRIx64"\n", buf, head);
>> -	pheader = (struct perf_event_header *)(buf + (head & mask));
>> -	*start = head;
>> +	pr_debug2("%s: buf=%p, start=%"PRIx64"\n", __func__, buf, *start);
>> +	pheader = (struct perf_event_header *)(buf + (*start & mask));
>>  	while (true) {
>> -		if (evt_head - head >= (unsigned int)size) {
>> +		if (evt_head - *start >= (unsigned int)size) {
>>  			pr_debug("Finished reading overwrite ring buffer: rewind\n");
>> -			if (evt_head - head > (unsigned int)size)
>> +			if (evt_head - *start > (unsigned int)size)
>>  				evt_head -= pheader->size;
>>  			*end = evt_head;
>>  			return 0;
>> @@ -287,7 +286,7 @@ int perf_mmap__read_init(struct perf_mmap *md, bool overwrite,
>>  		 * Backward ring buffer is full. We still have a chance to read
>>  		 * most of data from it.
>>  		 */
>> -		if (overwrite_rb_find_range(data, md->mask, head, startp, endp))
>> +		if (overwrite_rb_find_range(data, md->mask, startp, endp))
>>  			return -EINVAL;
>>  	}
>>  
>> -- 
>> 1.7.12.4
>>
> 
> .
>