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Mon, 10 Aug 2020 12:19:15 +0000 (UTC) Date: Mon, 10 Aug 2020 14:19:14 +0200 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH] Simple & stupid coroutine-aware monitor_cur() Message-ID: <20200810121914.GC14538@linux.fritz.box> References: <20200528153742.274164-1-kwolf@redhat.com> <20200528153742.274164-7-kwolf@redhat.com> <87tuxia5a9.fsf@dusky.pond.sub.org> <20200804160604.GB4860@linux.fritz.box> <87sgd15z5w.fsf@dusky.pond.sub.org> <87a6z6wqkg.fsf_-_@dusky.pond.sub.org> <87sgcyziul.fsf_-_@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87sgcyziul.fsf_-_@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/10 03:31:01 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , marcandre.lureau@gmail.com, qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 07.08.2020 um 15:27 hat Markus Armbruster geschrieben: > This is just a sketch. It's incomplete, needs comments and a real > commit message. > > Support for "[PATCH v6 09/12] hmp: Add support for coroutine command > handlers" is missing. Marked FIXME. > > As is, it goes on top of Kevin's series. It is meant to be squashed > into PATCH 06, except for the FIXME, which needs to be resolved in PATCH > 09 instead. > > Signed-off-by: Markus Armbruster > --- > monitor/monitor.c | 35 +++++++++++++++-------------------- > 1 file changed, 15 insertions(+), 20 deletions(-) > > diff --git a/monitor/monitor.c b/monitor/monitor.c > index 50fb5b20d3..8601340285 100644 > --- a/monitor/monitor.c > +++ b/monitor/monitor.c > @@ -82,38 +82,34 @@ bool qmp_dispatcher_co_shutdown; > */ > bool qmp_dispatcher_co_busy; > > -/* > - * Protects mon_list, monitor_qapi_event_state, coroutine_mon, > - * monitor_destroyed. > - */ > +/* Protects mon_list, monitor_qapi_event_state, * monitor_destroyed. */ > QemuMutex monitor_lock; > static GHashTable *monitor_qapi_event_state; > -static GHashTable *coroutine_mon; /* Maps Coroutine* to Monitor* */ > > MonitorList mon_list; > int mon_refcount; > static bool monitor_destroyed; > > +static Monitor **monitor_curp(Coroutine *co) > +{ > + static __thread Monitor *thread_local_mon; > + static Monitor *qmp_dispatcher_co_mon; > + > + if (qemu_coroutine_self() == qmp_dispatcher_co) { > + return &qmp_dispatcher_co_mon; > + } > + /* FIXME the coroutine hidden in handle_hmp_command() */ > + return &thread_local_mon; > +} Is thread_local_mon supposed to ever be set? The only callers of monitor_set_cur() are the HMP and QMP dispatchers, which will return something different. So should we return NULL insetad of thread_local_mon... > Monitor *monitor_cur(void) > { > - Monitor *mon; > - > - qemu_mutex_lock(&monitor_lock); > - mon = g_hash_table_lookup(coroutine_mon, qemu_coroutine_self()); > - qemu_mutex_unlock(&monitor_lock); > - > - return mon; > + return *monitor_curp(qemu_coroutine_self()); > } ...and return NULL here if monitor_curp() returned NULL... > void monitor_set_cur(Coroutine *co, Monitor *mon) > { > - qemu_mutex_lock(&monitor_lock); > - if (mon) { > - g_hash_table_replace(coroutine_mon, co, mon); > - } else { > - g_hash_table_remove(coroutine_mon, co); > - } > - qemu_mutex_unlock(&monitor_lock); > + *monitor_curp(co) = mon; ...and assert(monitor_curp(co) != NULL) here? This approach looks workable, though the implementation of monitor_curp() feels a bit brittle. The code is not significantly simpler than the hash table based approach, but the assumptions it makes are a bit more hidden. Saving the locks is more a theoretical improvement because all callers are slows paths anyway. Kevin