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. r~
