Alan Cox wrote: > On Fri, 30 Nov 2007 01:42:46 +0900 > Tejun Heo <htejun@xxxxxxxxx> wrote: > >> Alan Cox wrote: >>>> * Limit the amount of draining to ATAPI_MAX_DRAIN (16k currently). >>> Why 16 not 64K ? >> Oops, forgot to answer here. That would result in 16 sg entries for >> draining which felt a bit too much. > > 16 sg entries but only one page of memory so its not a bit bump ? The only added cpu cycle overhead is to setup sg entries and controller DMA table accordingly which should be pretty small. I was more worried about reserving that many sg entries as it can affect bulk data transfers. I thought about appending draining sg's on left-over SGs. ie. drain only min(nr_left_sgs, ATA_MAX_DRAIN_PAGES) pages but it ends up dereferencing deep upto request_queue and things get a bit complex because the way libata currently associates ata_device's with scsi_device's. So, I thought 16k was a good trade off. Not as comfortable as 64k tho, I agree. Would it be worth to add more complexity for this? Thanks. -- tejun - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
