On Wed, 12 Mar 2014, David Mosberger wrote: > So, quick question to the collective linux-usb wisdom: when I collect > a USB trace on my work-computer while running the command: > > dd if=/dev/zero of=/dev/sdX1 > > I see the same WRITE_10 commands of 122,880 bytes (240 sectors), but > the glaring difference is that each such WRITE_10 command seems to be > followed by ~ 27 READ_10 commands reading 1KB (2 sectors), whereas > with the MAX3421 driver, I see consecutive WRITE_10 commands. Anybody > know where those READ_10 commands are coming from?
I'd guess it's some sort of readahead. Not that it makes much sense to read sectors that are about to be overwritten. Did those READ commands occur before you started running dd? > Is it a cheap way > to poll the device if it's ready for the next block without having to > use expensive OUT transactions that get NAK'd? Definitely not. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
