On Tue, Dec 29, 2015 at 03:44:38PM +0200, Adrian Hunter wrote: > On 21/12/15 13:41, Russell King wrote: > > Unnecessarily mapping and unmapping the align buffer for SD cards is > > expensive: performance measurements on iMX6 show that this gives a hit > > of 10% on hdparm buffered disk reads. > > > > MMC/SD card IO comes from the mm/vfs which gives us page based IO, so > > for this case, the align buffer is not going to be used. However, we > > still map and unmap this buffer. > > > > Eliminate this by switching the align buffer to be a DMA coherent > > buffer, which needs no DMA maintenance to access the buffer. > > Did you consider putting the align buffer in the same allocation > as the adma_table? It's not clear whether host->adma_table_sz would be appropriately aligned. > > @@ -3003,6 +2972,10 @@ int sdhci_add_host(struct sdhci_host *host) > > host->adma_table_sz, > > &host->adma_addr, > > GFP_KERNEL); > > + host->align_buffer = dma_alloc_coherent(mmc_dev(mmc), > > + host->align_buffer_sz, > > + &host->align_addr, > > + GFP_KERNEL); > > host->align_buffer = kmalloc(host->align_buffer_sz, GFP_KERNEL); > > kmalloc line is still there Good catch, thanks. > > + > > + /* dma_alloc_coherent returns page aligned and sized buffers */ > > + BUG_ON(host->align_addr & host->align_mask); > > It would be nicer not to have any BUG_ON() This is a situation that should _never_ occur (if it does, then the dma_alloc_coherent() implementation is violating the API requirements, which are to return a page-sized page-aligned buffer.) I guess it could be a WARN_ON(), but if it fails we're likely to cause data corruption. So, a WARN_ON() and failing the probe seems more appropriate - but then that means yet more messy cleanup in an already messy part of the driver. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- 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
