Am 17.09.18 um 18:30 schrieb Emilio G. Cota: > This series comes originally from a series of patches that Paolo > sent to me a long time ago. I have kept most of his S-o-b tags, > but I have done the forward port of the patches to the current > QEMU code base, so please blame all possible bugs on me, not him. > > The goal of this series is to push the BQL out of interrupt > handling wherever possible. Many targets do not need the BQL > to handle interrupts, so for those targets we get rid of the > BQL in interrupt handling. In TCG mode, this by itself does > not yield measurable performance gains. However, it is a > necessary first step before tackling BQL contention when > managing CPU states (i.e. exiting the exec loop always > involves taking the BQL, which does not scale). > > The patches: > > - Patch 0 accesses icount_decr.u16 consistently with atomics. > This is important because we use it across threads to signal > that an interrupt is pending. > > - 2-28: convert direct callers of cpu->interrupt_request > to use atomic accesses or CPU helper functions that use atomics. > I have broken these up into individual patches to ease review. > Note that in some cases I have added many atomic_reads, most > of which are probably unnecessary. However, I'd leave this up > to the maintainers, since I do not want to break things by > doing a single atomic_read(&cpu->interrupt_request) at the > beginning of a function and then miss subsequent updates to > cpu->interrupt_request. > > - 29-31: drop the BQL requirement when handling cpu->interrupt_request > > - 32-33: drop now unnecessary BQL acquisitions in i386 and ppc > > - 34-35: push down the BQL acquisition to cpu->do_interrupt > and cpu->cpu_exec_interrupt. Here I am Cc'ing everyone so that > we can make sure I am not missing any target that requires > the BQL on either do_interrupt or cpu_exec_interrupt. > > This series is checkpatch-clean, and can be fetched from: > https://github.com/cota/qemu/tree/cpu-lock > > Note that the series applies on top of patches that are > already on the qemu-devel list and will hopefully soon > be upstream. This series begins after commit > 4ece0cbd74 ("cpus: access .qemu_icount_bias with atomic64") > in that tree. > > Thanks, > > Emilio > I just did a (very slow) make -j32 of QEMU on my 16 core notebook inside a MTTCG s390x-softmmu guest with 32 VCPUs. I used the same test when reworking floating interrupt support to make sure there are no races. As I got no deadlock, I assume you series does not break anything for s390x. Thanks! -- Thanks, David / dhildenb
