On Tue, Jan 09 2007, Vasily Tarasov wrote: > Jens Axboe wrote: > > On Tue, Jan 09 2007, Vasily Tarasov wrote: > > > >> Jens Axboe wrote: > >> > >>> Tom, you are correct, the 'B' is a bounce and not a backmerge. Vasily, > >>> you may want to look into your setup, bouncing is very harmful to io > >>> performance. > >>> > >>> > >>> > >> Hello again, > >> > >> My node has 4GB RAM and by default block queue limit > >> is high memory boundary: > >> blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH); > >> Driver doesn't set other bounce limit (like most drivers), > >> so I have bounces. > >> > >> Seems, that all people with more then 1GB Memory > >> should have such situation (except lucky beggars with "appropriate" > >> drivers), > >> am I right? > >> > > > > What driver do you use? By far the most common ones do support highmem > > IO (like IDE/SATA/SCSI, etc). > > > > > My driver is NVIDIA Serial ATA.
SATA/libata defaults to a full 32-bit dma mask, so it doesn't impose any bounce restrictions. If the pci device has set a lower limit, then that one applies of course. It's quite unusual to have bouncing hardware in hardware from recent years, unless it's a buggy piece of hardware (or we don't know how to drive upper limits, due to lack of documentation). You should look into why and who sets a lower mask for your device. Note that the default limit is only active, until SCSI+libata configures a queue and the slave config sets the limit again. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-btrace" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
