On 2014-05-23 06:48, Jiri Horky wrote:
Hi all,
because I got bitten by this multiple times I decided to give this patch
a try :)
Current implementation of offset calculation when offset_increment is in
effect uses global thread_number as follows:
f->file_offset = td->o.start_offset + (td->thread_number - 1) *
td->o.offset_increment;
The thread number gets incremented for every job (subjob) so even you
have multiple jobs with different filenames, the offset calculation is
shared. I find this very unintuitive, especially in cases the offsets
gets past the device/file. For example, if one wants to run sequential
read test in 16 threads of multiple devices (/dev/sd{b,c,d}) in one
group, which are of 1TB size, and to eliminate caching effect he wants
each read to start at different offset, the config could look like
following:
Maybe it would be better to have this offset calculation be on a
per-thread-per-file basis? You are right in that it only makes sense
within the same file or device, so maybe it'd be better to make it work
more like you expect.
--
Jens Axboe
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