On Fri, Oct 21, 2016 at 03:08:09PM +0900, Sergey Senozhatsky wrote: > Hello Minchan, > > On (10/17/16 14:04), Minchan Kim wrote: > > Hi Sergey, > > > > On Fri, Oct 07, 2016 at 03:33:22PM +0900, Minchan Kim wrote: > > > > < snip > > > > > > > so the question is -- can we move this parallelization out of zram > > > > and instead flush bdi in more than one kthread? how bad that would > > > > be? can anyone else benefit from this? > > > > > > Isn't it blk-mq you mentioned? With blk-mq, I have some concerns. > > > > > > 1. read speed degradation > > > 2. no work with rw_page > > > 3. more memory footprint by bio/request queue allocation > > > > > > Having said, it's worth to look into it in detail more. > > > I will have time to see that approach to know what I can do > > > with that. > > > > queue_mode=2 bs=4096 nr_devices=1 submit_queues=4 hw_queue_depth=128 > > > > Last week, I played with null_blk and blk-mq.c to get an idea how > > blk-mq works and I realized it's not good for zram because it aims > > to solve 1) dispatch queue bottleneck 2) cache-friendly IO completion > > through IRQ so 3) avoids remote memory accesses. > > > > For zram which is used for embedded as primary purpose, ones listed > > abvoe are not a severe problem. Most imporant thing is there is no > > model to support that a process queueing IO request on *a* CPU while > > other CPUs issues the queued IO to driver. > > > > Anyway, Although blk-mrq can support that model, it is blk-layer thing. > > IOW, it's software stuff for fast IO delievry but what we need is > > device parallelism of zram itself. So, although we follow blk-mq, > > we still need multiple threads to compress in parallel which is most of > > code I wrote in this patchset. > > yes. but at least wb can be multi-threaded. well, sort of. seems like. > sometimes. Maybe, but it would be rather greedy approach for zram because zram will do real IO(esp, compression which consumed a lot of time) in that context although the context is sharable resource of all processes in the system. > > > If I cannot get huge benefit(e.g., reduce a lot of zram-speicif code > > to support such model) with blk-mq, I don't feel to switch to request > > model at the cost of reasons I stated above. > > thanks. > I'm looking at your patches. Currently, I found some subtle bug in my patchset so I will resend them after hunting that with fixing a bug you found. Thanks, Sergey! -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
