>>>>> "Finn" == Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> writes: Finn> Large PIO transfers are broken up into chunks to try to avoid Finn> disabling local IRQs for long periods. But IRQs are still disabled Finn> for too long and this causes SCC FIFO overruns during serial port Finn> transfers. Finn> This patch reduces the PIO chunk size to reduce interrupt latency Finn> to something on the order of milliseconds, at the expense of Finn> additional CPU overhead from extra iterations of the Finn> NCR5380_main() loop. Finn> That CPU overhead is a problem for slow machines (e.g. mac_scsi on Finn> 25 MHz Finn> 68030) but these machines generally use PDMA not PIO. This patch Finn> doesn't Finn> make the overhead any worse on my Mac LC III (because it only gets Finn> about 510 accesses per ms). Finn> This patch decreases disk performance by a fraction of one percent Finn> for dmx3191d on my 333 MHz PowerPC 750. Other affected hardware Finn> (such as g_NCR5380 on x86) was not tested but 5380 ISA cards Finn> generally use PDMA and not PIO. Geert? -- Martin K. Petersen Oracle Linux Engineering -- 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
