On Feb 4, 2008 1:27 PM, Vladislav Bolkhovitin <vst@xxxxxxxx> wrote: > > So, James, what is your opinion on the above? Or the overall SCSI target > project simplicity doesn't matter much for you and you think it's fine > to duplicate Linux page cache in the user space to keep the in-kernel > part of the project as small as possible? It's too early to draw conclusions about performance. I'm currently performing more measurements, and the results are not easy to interpret. My plan is to measure the following: * Setup: target with RAM disk of 2 GB as backing storage. * Throughput reported by dd and xdd (direct I/O). * Transfers with dd/xdd in units of 1 KB to 1 GB (the smallest transfer size that can be specified to xdd is 1 KB). * Target SCSI software to be tested: IETD iSCSI via IPoIB, STGT iSCSI via IPoIB, STGT iSER, SCST iSCSI via IPoIB, SCST SRP, LIO iSCSI via IPoIB. The reason I chose dd/xdd for these tests is that I want to measure the performance of the communication protocols, and that I am assuming that this performance can be modeled by the following formula: (transfer time in s) = (transfer setup latency in s) + (transfer size in MB) / (bandwidth in MB/s). Measuring the time needed for transfers with varying block size allows to compute the constants in the above formula via linear regression. One difficulty I already encountered is that the performance of the Linux IPoIB implementation varies a lot under high load (http://bugzilla.kernel.org/show_bug.cgi?id=9883). Another issue I have to look further into is that dd and xdd report different results for very large block sizes (> 1 MB). Bart Van Assche. - 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
