Hi peter: i see, much, much helpfull. thank you! :).
At 2024-04-09 18:51:26, "Peter Maydell" <peter.mayd...@linaro.org> wrote: >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
