On Tue, 22 Dec 2015 12:18:44 +1100 Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote: > Because of the rudimentary design of the chip, it is necessary to poll the > SCSI bus signals during PIO and this tends to hog the CPU. The driver will > accept new commands while others execute, and this causes a soft lockup > because the workqueue item will not terminate until the issue queue is > emptied. > > When exercising dmx3191d using sequential IO from dd, the driver is sent > 512 KiB WRITE commands and 128 KiB READs. For a PIO transfer, the rate is > is only about 300 KiB/s, so these are long-running commands. And although > PDMA may run at several MiB/s, interrupts are disabled for the duration > of the transfer. > > Fix the unresponsiveness and soft lockup issues by calling cond_resched() > after each command is completed and by limiting max_sectors for drivers > that don't implement real DMA. Is there a reason for not doing some limiting in the DMA case too. A 512K write command even with DMA on a low end 68K box introduces a second of latency before another I/O can be scheduled ? Alan -- 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
