On Sun, 20 Jan 2008 10:36:18 +0100 "Bart Van Assche" <bart.vanassche@xxxxxxxxx> wrote: > On Jan 18, 2008 1:08 PM, Vladislav Bolkhovitin <vst@xxxxxxxx> wrote: > > > > [ ... ] > > So, seems I understood your slides correctly: the more valuable data for > > our SCST SRP vs STGT iSER comparison should be on page 26 for 1 command > > read (~480MB/s, i.e. ~60% from Bart's result on the equivalent hardware). > > At least in my tests SCST performed significantly better than STGT. > These tests were performed with the currently available > implementations of SCST and STGT. Which performance improvements are First, I recommend you to examine iSER stuff more since it has some parameters unlike SRP, which effects the performance, IIRC. At least, you could get the iSER performances similar to Pete's. > possible for these projects (e.g. zero-copying), and by how much is it > expected that these performance improvements will increase throughput > and will decrease latency ? The major bottleneck about RDMA transfer is registering the buffer before transfer. stgt's iSER driver has pre-registered buffers and move data between page cache and thsse buffers, and then does RDMA transfer. The big problem of stgt iSER is disk I/Os (move data between disk and page cache). We need a proper asynchronous I/O mechanism, however, Linux doesn't provide such and we use a workaround, which incurs large latency. I guess, we cannot solve this until syslets is merged into mainline. The above approach still needs one memory copy (between the pre-registered buffers and page cahce). If we need more performance, we have to implement a new caching mechanism using the pre-registered buffers instead of just using page cache. AIO with O_DIRECT enables us to implement such caching mechanism (we can use eventfd so we don't need something like syslets, that is, we can implement such now). I'm not sure someone will implement such RDMA caching mechanism for stgt. Pete and his colleagues implemented stgt iSER driver (thanks!) but they are not interested in block I/Os (they are OSD people). - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
