On 09/09/2015 12:41, Juan Quintela wrote: >> > + qemu_mutex_unlock_iothread(); >> > + atomic_set(&cpu->throttle_thread_scheduled, 0); >> > + g_usleep(sleeptime_ns / 1000); /* Convert ns to us for usleep call */ >> > + qemu_mutex_lock_iothread(); > > Why is this thread safe? > > qemu_mutex_lock_iothread() is protecting (at least) cpu_work_first on > each cpu. How can we be sure that _nothing_ will change that while we > are waiting?
You only have to be sure that the queued work list remains consistent; not that nothing changes. (BTW, there is a queued patch that moves the queued work list to its own mutex, and indeed it releases that mutex while calling the work function). > A fast look through the tree don't show anything that > runs here that drops the lock. Actually, the existing implementation of throttling does. :) Paolo
