Re: what is the sample logger doing when the buffer fills up?

[Jens Axboe <axboe@kernel.dk>]

On Wed, Jul 06 2016, Karl Cronburg wrote:
> Hello all,
> 
> When I change add_clat_sample() in stat.c to call add_log_sample() seven times
> instead of once, and I set DEF_LOG_ENTRIES=4096, I get the following in the clat
> log file (note first column is line number in the file):
> 
>   4089 143, 9832, 0, 131072
>   4090 143, 9832, 0, 131072
>   4091 143, 9832, 0, 131072
>   4092 143, 9832, 0, 131072
>   4093 143, 9832, 0, 131072
>   4094 143, 9832, 0, 131072
>   4095 143, 9832, 0, 131072
>   4096 143, 9834, 0, 131072
>   4097 170, 15982, 0, 131072
>   4098 170, 15982, 0, 131072
>   4099 170, 15982, 0, 131072
>   4100 170, 15982, 0, 131072
>   4101 170, 15982, 0, 131072
>   4102 170, 15982, 0, 131072
>   4103 170, 15982, 0, 131072
>   4104 170, 15985, 0, 131072
>   4105 170, 15985, 0, 131072
> 
> Notice the lonely '9834' value in the center, which should have 7
> exact copies of itself
> but gets cut off right at the buffer size of 4096 entries.
> 
> So if I'm interpreting this correctly, samples get silently dropped
> (or not properly printed?)
> when the buffer fills up. Is this a bug? Am I misinterpreting what the
> doubly linked list is
> for? I was under the impression that a new sample buffer should be
> added to the linked
> list when the current one fills up.

Fair to assume this is what your patch fixed, correct? Just wanted to
ensure that it's already fixed.

-- 
Jens Axboe