On Mon, Feb 12, 2007 at 02:08:10PM +0100, Andi Kleen (ak@xxxxxxx) wrote: > Evgeniy Polyakov <johnpol@xxxxxxxxxxx> writes: > > > > aio_sendfile_path() is essentially aio_sendfile(), except that it takes > > source filename as parameter, has a pointer to private header > > and its size (which allows to send header and file's content in one syscall > > instead of three (open, send, sendfile) and returns opened file descriptor. > > Are you sure this is a useful optimization? Do you have numbers vs open+aio_sendfile+close? > > Compared to the cost of sending a complete file three system calls should be quite in the noise. > And Linux system calls are not that expensive (few hundred cycles normally) > > Adding such compound system calls would be a worrying precedent because > I'm sure others would want them then for their favourite system call combo > too. If they were really useful it might make more sense to have a batch() > system call that works for arbitary calls, but I'm not convinced yet > it's even needed. It would be certainly ugly. Yes, that call ends up about 10MB/sec faster for 100 1mb file transfers over 1gbit network (78 MB/s vs 66-72 MB/s over 1 Gb network, sendfile sending server is one-way AMD Athlong 64 3500+), but indeed, it can be the case that async IO sending was main speed factor. I added header by request from Suparna Bhattacharya - my main position is the same about syscall overhead, but I do not that care. > -Andi -- Evgeniy Polyakov - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
