On Tue, 9 Apr 2024 at 11:40, tugouxp <13824125...@163.com> wrote: > ===>yes, i somehow a little bit of guess such like that, but when try to find > some code in qemu to prove the guess, i found i was lost and exausted in the > ocean of the code and complex logic of qeumu. > because in my thougth, it may be do the sync in user pthread level, so i grep > the "pthread" "mutex", "condtion",... and so on, but did not find any > position to prove this thought. > so, can you offer me the demo code position of do the sync like "pause > execution of all the other guest vCPU threads,", to make the atomic > operations meet the sematics?
I would suggest starting by translating some guest code with the atomic operation you're interested in, and using the '-d' suboptions in_asm, op and out_asm to look at the generated TCG operations and the generated host code for it. The stop-the-world handling happens when something calls cpu_loop_exit_atomic(), which then raises an EXCP_ATOMIC internal-to-QEMU exception, which is handled by some top-level-loop code that calls cpu_exec_step_atomic(), which (a) uses start_exclusive() and end_exclusive() to ensure that it is the only vcpu running and (b) generates new host code with the CF_PARALLEL flag clear to tell the translator that it can assume it's the only thing running (which in turn means "you don't need to actually do this operation atomically"). thanks -- PMM
