Jens Axboe wrote: > 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. > Thanks for advices, I'll definitely try it and inform you.
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