On Fri, Jan 11, 2019 at 2:09 PM Richard Henderson <richard.hender...@linaro.org> wrote: > > On 1/12/19 9:01 AM, Max Filippov wrote: > > Don't invalidate TB with the end of zero overhead loop when LBEG or LEND > > change. Instead encode the distance from the start of the page where the > > TB starts to the LEND in the TB cs_base and generate loopback code when > > the next PC matches encoded LEND. Distance to a destination within the > > same page and up to a maximum instruction length into the next page is > > encoded literally, otherwise it's zero. The distance from LEND to LBEG > > is also encoded in the cs_base: it's encoded literally when less than > > 256 or as 0 otherwise. This allows for TB chaining for the loopback > > branch at the end of a loop for the most common loop sizes. > > > > With this change the resulting emulation speed is about 10% higher in > > softmmu mode on uClibc-ng and LTP tests. Emulation speed in linux > > user mode is a few percent lower because there's no direct TB chaining > > between different memory pages. Testing with lower limit on direct TB > > chainig range shows gradual slowdown to ~15% for the block size of 64 > > bytes and ~50% for the block size of 32 bytes. > > > > Signed-off-by: Max Filippov <jcmvb...@gmail.com> > > Reviewed-by: Richard Henderson <richard.hender...@linaro.org> > > > > + /* > > + * 0 in the csbase_lend field means that there may not be a > > loopback > > + * for any instruction that starts inside this page. Any other > > value > > + * means that an instruction that ends at this offset from the page > > + * start may loop back. > > Nit: s/may/will/g > > Using "may" makes it seem like we may have missed a case that should have > looped back.
Using "will" makes it seem like it always loops back, but it doesn't do it when LCOUNT is 0. -- Thanks. -- Max