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icount: improve exec nocache usage 

cpu-exec tries to execute TB without caching when current
icount budget is over. But sometimes refilled budget is big
enough to try executing cached blocks.
This patch checks that instruction budget is big enough
for next block execution instead of just running cpu_exec_nocache.
It halves the number of calls of cpu_exec_nocache function
during tested OS boot scenario.

Signed-off-by: Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>
Message-Id: <160741865825.348476.7169239332367828943.stgit@pasha-ThinkPad-X280>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Pavel Dovgalyuk 2020-12-08 12:10:58 +03:00 committed by Paolo Bonzini
parent 90d6a086bb
commit 835cbd8d44
1 changed files with 1 additions and 1 deletions
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2
accel/tcg/cpu-exec.c
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@ -685,7 +685,7 @@ static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
insns_left = MIN(0xffff, cpu->icount_budget);
cpu_neg(cpu)->icount_decr.u16.low = insns_left;
cpu->icount_extra = cpu->icount_budget - insns_left;
if (!cpu->icount_extra) {
if (!cpu->icount_extra && insns_left < tb->icount) {
/* Execute any remaining instructions, then let the main loop
* handle the next event.
*/