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. Hello,
I got the very interesting situation! blk_max_pfn = max_pfn = 1048576 while SCSI/libata driver sets q->bounce_pfn = 1048575 Thus I have a bunch of bounces. The main question for me now is why max_pfn = 1048576? I suppose that it should be equal to 1048575 on my 4GB RAM mashine: (4 x 1024 x 1024 x 1024) / (4 x 1024) = 1024 x 1024 = 1048576 - this is total number of page frames. But, max_pfn should be equal 1048576 - 1 = 1048575. What do you think? Thanks, Vasily. - 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
