linux-kernel - Re: [PATCH] perf mmap: Discard head in overwrite_rb_find

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Date:   Thu, 8 Mar 2018 09:05:40 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>
CC:     <mingo@...hat.com>, <peterz@...radead.org>, <namhyung@...nel.org>,
        <acme@...nel.org>, <alexander.shishkin@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [PATCH] perf mmap: Discard head in overwrite_rb_find_range

Hi Arnaldo,

On 2018/3/7 21:58, Arnaldo Carvalho de Melo wrote:
> Em Wed, Mar 07, 2018 at 11:21:57AM +0100, Jiri Olsa escreveu:
>> 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
> 
> yeah, wait a while till I push Kan's simplifications and then resubmit,
> ok?
> 
Sure, I will wait and resubmit.

Thanks
Yisheng

> - Arnaldo
>  
>> jirka
>>
>>>
>>> Signed-off-by: Yisheng Xie <xieyisheng1@...wei.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
>>>
> 
> .
>