On Wed, Sep 19, 2018 at 01:59:53PM -0600, Jens Axboe wrote: > On 9/19/18 1:56 PM, Dennis Zhou wrote: > > On Wed, Sep 19, 2018 at 12:49:15PM -0600, Jens Axboe wrote: > >> On 9/19/18 12:25 PM, Dennis Zhou wrote: > >>> As we explore stacking traces, it is nice to be able to scale a trace to > >>> understand how the traces end up interacting. > >>> > >>> This patch adds scaling by letting the user pass in percentages to scale > >>> a trace by. When passed '--merge_blktrace_scalars="100", the trace is > >>> ran at 100% speed. If passed 50%, this will halve the trace timestamps. > >>> The new option takes in a comma separated list that index-wise pairs > >>> with the passed files in "--read_iolog". > >> > >> How is this different than replay_time_scale? > >> > > > > I think merge_blktrace_scalars is a trace building parameter whereas > > replay_time scale is a runtime parameter. merge_blktrace_scalars is an > > index-paired list with the logs passed to --read_iolog allowing for each > > trace to be independently scaled. replay_time_scale happens at runtime > > and scales the entire trace uniformly. And because replay_time_scale > > happens at runtime, I'm not sure repurposing the numbers would be super > > intuitive. > > Not sure I see the difference, if you just allow replay_time_scale to > take multiple values (one for each trace)? > I'm imagining if I reused replay_time_scale, I could use those numbers for merging, but then I'd have to reset it so that it doesn't affect the trace a second time during runtime. I feel like this gets a little weird as we're saying if you are merging, replay_time_scale gets applied during the merge, otherwise it gets applied during runtime. Reusing also makes it become a many (merging) to one (runtime) parameter change too as merging works on multiple files (main thread) while runtime runs a single file (worker thread). Additionally, I don't think it's unreasonable to want to store the merged trace in realtime and then run the merged trace at a different pace, which would require the merge time and runtime knobs to be different. Thanks, Dennis
