On 09/18/2013 08:41 AM, Alireza Haghdoost wrote: > Hi > > I am working on a high throughput and low latency application which > does not tolerate block layer overhead to send IO request directly to > fiber channel lower layer SCSI driver. I used to work with libaio but > currently I am looking for a way to by pass the block layer and send > SCSI commands from the application layer directly to the SCSI driver > using /dev/sgX device and ioctl() system call. > > I have noticed that sending IO request through sg device even with > nonblocking and direct IO flags is quite slow and does not fill up > lower layer SCSI driver TCQ queue. i.e IO depth or > /sys/block/sdX/in_flight is always ZERO. Therefore the application > throughput is even lower that sending IO request through block layer > with libaio and io_submit() system call. In both cases I used only one > IO context (or fd) and single threaded. > Hi Alireza, I think what you want is in_flight command scsi dispatch to low level device. I submit a simple patch to export device_busy http://www.spinics.net/lists/linux-scsi/msg68697.html I also notice fio sg engine will not fill queue properly, but haven't look into deeper. Cheers Jack > I have noticed that some well known benchmarking tools like fio does > not support IO depth for sg devices as well. Therefore, I was > wondering if it is feasible to bypass block layer and achieve higher > throughput and lower latency (for sending IO request only). > > > Any comment on my issue is highly appreciated. > > > Thanks > Alireza > -- > 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
