On Thu, Feb 28, 2013 at 03:38:44PM +1030, Rusty Russell wrote: > "Michael S. Tsirkin" <mst@xxxxxxxxxx> writes: > > On Fri, Feb 22, 2013 at 10:32:46AM +1030, Rusty Russell wrote: > >> "Michael S. Tsirkin" <mst@xxxxxxxxxx> writes: > >> > On Tue, Feb 19, 2013 at 06:26:26PM +1030, Rusty Russell wrote: > >> >> These are specialized versions of virtqueue_add_buf(), which cover > >> >> over 50% of cases and are far clearer. > >> >> > >> >> In particular, the scatterlists passed to these functions don't have > >> >> to be clean (ie. we ignore end markers). > >> >> > >> >> FIXME: I'm not sure about the unclean sglist bit. I had a more > >> >> ambitious one which conditionally ignored end markers in the iterator, > >> >> but it was ugly and I suspect this is just as fast. Maybe we should > >> >> just fix all the drivers? > >> >> > >> >> Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx> > >> > > >> > Looking at code, it seems that most users really have a single sg, in > >> > low memory. So how about simply passing void * instead of sg? Whoever > >> > has multiple sgs can use the rich interface. > >> > >> Good point, let's do that: > >> 1) Make virtqueue_add_outbuf()/inbuf() take a void * and len. > >> 2) Transfer users across to use that. > >> 3) Make everyone else use clean scatterlists with virtqueue_add_sgs[]. > >> 4) Remove virtqueue_add_bufs(). > >> > >> > Long term we might optimize this unrolling some loops, I think > >> > I saw this giving a small performance gain for -net. > >> > >> I *think* we could make virtqueue_add() an inline and implement an > >> virtqueue_add_outsg() wrapper and gcc will eliminate the loops for us. > >> But not sure it's worth the text bloat... > >> > >> Cheers, > >> Rusty. > > > > inline is mostly useless nowdays... We can make it a static function and > > let gcc decide. > > I know I've said before that inline is the register keyword of the '90s. > But not at -O2 with i686-linux-gnu-gcc-4.7 (Ubuntu/Linaro > 4.7.2-2ubuntu1) 4.7.2. > > Without the inline keywords, it doesn't inline virtqueue_add, and thus > sg_next_chained and sg_next_add aren't inlined: > > $ for i in `seq 50`; do /usr/bin/time --format=%U ./vringh_test --indirect --eventidx --parallel; done 2>&1 | stats --trim-outliers > Using CPUS 0 and 3 > Guest: notified 39102-39145(39105), pinged 39060-39063(39063) > Host: notified 39060-39063(39063), pinged 19551-19581(19553) > 3.050000-3.220000(3.136875) > > With inline: > > $ for i in `seq 50`; do /usr/bin/time --format=%U ./vringh_test --indirect --eventidx --parallel; done 2>&1 | stats --trim-outliers > Using CPUS 0 and 3 > Guest: notified 39084-39148(39099), pinged 39062-39063(39062) > Host: notified 39062-39063(39062), pinged 19542-19574(19550) > 2.940000-3.140000(3.014583) > > Cheers, > Rusty. Cool and did it actually unroll all loops? _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
