<div dir="ltr">I don't remember the details of how we did the sync in XCB back when: we did something very like what you are doing, but the details are a bit tricky to get right. In particular, XCB will only send an input focus request when no request (not just input focus) has received a reply in the last 64K requests. So...yeah. It's been literally a decade since I looked at this stuff, but I *think* you should be able to dig the last-sync count out of XCB and just work from that: probably can just use the XCB code or at least algorithm to tell you when to sync. We had a correctness proof at one point. We had it again after we found and fixed a bug in the proof. :-)</div> <div class="gmail_quote"><div dir="ltr">On Thu, Dec 28, 2017 at 11:39 AM Clemens Eisserer <<a href="mailto:linuxhippy@gmail.com">linuxhippy@gmail.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Bart, > The overhead of doing separate XShmPutImages should be minimal. Xcb is performing fine, what is causing performance issues is how the drivers implement those tiny XPutImage requests (especially when operating on top of OpenGL like all glamor based setups). I've found a way to implement the deferred protocol submission using the socket handoff mechanism and it seems to work really well. However, currently the socket owner changes quite frequently, so I am struggling with the requirement to issue a XGetInputFocus-Request *every* time I call xcb_take_socket. For cases where there are only 4 requests to submit, an additional XGetInputFocus hurts. What I tried instead was: uint64_t lastManualSyncSeq; //Remember sequence-number, when the last manual sync was issued uint64_t socketTakenSeq; //Sequence number when the socket was taken uint32_t self_generated_count; //Number of self-generated X requests while(1) { xcb_take_socket(xcbCon, &returnSocketCB, &flags, 0, &socketTakenSeq); while(1) { if((socketTakenSeq + self_generated_count) - lastManualSyncSeq > 65000) { //will cause socket to be revoked, callback will take care of flushing out generated protocol lastManualSyncSeq = xcb_get_input_focus(xcbCon).sequence; xcb_discard_reply(xcbCon, lastManualSyncSeq); self_generated_count = 0; break; } self_generated_count++; GenerateXrenderFillRectanglesRequest(); //appends reply-less request to request data buffer } The idea is I can't be sure when xcb automatically generated the last XGetInputFocus request, but I know when I last called xcb_get_input_focus myself. As long as the last call to xcb_get_input_focus is less than 65k requests away, everything is fine (regardless of whether xcb issued some xcb_get_input_focus requests in between). However, this doesn't seem to work out as expected - I still get hangs from time to time. Any idea what is wrong with the above snippit? Thank you in advance, Clemens </blockquote></div>