On 04/09/2010 08:07 AM, Gao, Yunpeng wrote:
Hi,
I'm working on a block device driver (NAND flash driver with FTL layer) on
2.6.31 Kernel. And try to improve sequential read/write performance of the
block driver.
When I debug the driver, I found that the sector numbers of every r/w request
in the request queue is always not bigger than 8. That means, for every r/w
request, it only handle 512 * 8 = 4KB bytes at most. And I think the sequential
r/w speed can be improved if the Linux block layer generates bigger size data
(for example, 64KB) for every request in the request queue.
To implement this, I have added some code as below (My hardware doesn't support
scatter/gather, but can do 512KB DMA data transfer):
...
blk_queue_max_sectors(dev->queue, 1024);
blk_queue_max_phys_segments(dev->queue, 128);
blk_queue_max_hw_segments(dev->queue, 1);
blk_queue_max_segment_size(dev->queue, 524288);
...
And also set NOOP as the default IO Scheduler (because the underlying 'block'
device is NAND flash, not a real hard disk).
But seems it doesn't work. The block layer still generate at most 8 sector r/w
request in request queue even if I read/write 1GB data from/to the device with
dd command.
Did I miss something to make the block layer generate bigger size data for
every request in the request queue?
Below is part of my source code. Any comments are highly appreciated. Thank you
in advance.
8 sectors is 4KB, that's the size of a page. If the pages that are being
written are not physically contiguous that may be the best the block
layer can do with the constraints you've given it (not supporting any
more than 1 DMA segment). I don't think it will try to copy pages around
in order to try and generate a bigger request.
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