Will Newton <will.newton@xxxxxxxxx> wrote: > On Thu, Feb 23, 2012 at 11:58 PM, Seungwon Jeon <tgih.jun@xxxxxxxxxxx> wrote: > > Will Newton <will.newton@xxxxxxxxx> wrote: > >> 2012/2/23 Seungwon Jeon <tgih.jun@xxxxxxxxxxx>: > >> > Hi all, > >> > > >> > Even though 1MB is reserved for descriptor table in IDMAC, > >> > the dw_mmc host driver is allowed to receive only maximum > >> > 128KB block length in one request. This is caused by setting > >> > improper max_blk_count. It needs to be e adjusted so that > >> > descriptor table is used fully. > >> > > >> > It is found that the performance is improved with the increased the > >> > max_blk_count. In my case, there is 82%(6%) improvement in sequential > >> > write(read). Is there anybody who knows the reason about the old setting? > >> > > >> > Best regards, > >> > Seungwon Jeon. > >> > > >> > Signed-off-by: Seungwon Jeon <tgih.jun@xxxxxxxxxxx> > >> > --- > >> > drivers/mmc/host/dw_mmc.c | 4 ++-- > >> > 1 files changed, 2 insertions(+), 2 deletions(-) > >> > > >> > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c > >> > index bf3c9b4..af2b901 100644 > >> > --- a/drivers/mmc/host/dw_mmc.c > >> > +++ b/drivers/mmc/host/dw_mmc.c > >> > @@ -1804,9 +1804,9 @@ static int __init dw_mci_init_slot(struct dw_mci *host, unsigned int id) > >> > #ifdef CONFIG_MMC_DW_IDMAC > >> > mmc->max_segs = host->ring_size; > >> > mmc->max_blk_size = 65536; > >> > - mmc->max_blk_count = host->ring_size; > >> > mmc->max_seg_size = 0x1000; > >> > - mmc->max_req_size = mmc->max_seg_size * mmc->max_blk_count; > >> > + mmc->max_req_size = mmc->max_seg_size * host->ring_size; > >> > + mmc->max_blk_count = mmc->max_req_size / 512; > >> > >> I am not sure this is correct, it seems like most drivers calculate > >> max_req_size like this: > >> > >> mmc->max_req_size = mmc->max_blk_size * mmc->max_blk_count; > > > > Could you explain the following origin code in dw_mmc? > > We need to change like most other drivers? > > mmc->max_req_size = mmc->max_seg_size * mmc->max_blk_count; > > All the other drivers seem to set max_req_size based on blk_size and > blk_count not seg_size so the current code looks like it may be wrong. Then, How can determine the blk_count? max_req_size is a limitation which should be submitted to mmc stack. dw_mmc can transfer the data as max_req_size with the DMA descriptors. So I think max_seg_size and ring_size are good information for max_req_size in IDMAC and current setting of mmc->max_req_size is fine. > > > - mmc->max_blk_count is set as host->ring_size. > > - max_seg_size seems to represent max_blk_size. > > I believe max_seg_size should be set to a higher value as it appears > to be only relevant for IOMMU-based drivers, possibly the same as > max_req_size. As we can refer kernel/block, several segments of max_seg_size make up a request ,which has hardware sectors in the usual 512b unit. Max hardware sectors can be offered to block layer like the following in drivers/mmc/card/queue.c. blk_queue_max_hw_sectors(mq->queue, min(host->max_blk_count, host->max_req_size / 512)); That means "host->max_blk_count" or "host->max_req_size / 512" decides the max request size. So we need to set the proper max-blk_count. This RFC patch is intended for that. Thanks, Seungwon Jeon. > -- > To unsubscribe from this list: send the line "unsubscribe linux-mmc" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
