On 11/21/2019 12:26 PM, Jackie Liu wrote: > 2019年11月21日 16:54，Pavel Begunkov <asml.silence@xxxxxxxxx> 写道： >> >> If there is a DRAIN in the middle of a link, it uses shadow req. Defer >> the next request/link instead. This: >> >> Pros: >> 1. removes semi-duplicated code >> 2. doesn't allocate memory for shadows >> 3. works better if only the head marked for drain > > I thought about this before, just only drain the head, but if the latter IO depends > on the link-list, then latter IO will run in front of the link-list. If we think it > is acceptable, then I think it is ok for me. If I got your point right, latter requests won't run ahead of the link-list. There shouldn't be change of behaviour. The purpose of shadow requests is to mark some request right ahead of the link for draining. This patch uses not a specially added shadow request, but the following regular one. And, as drained IO shouldn't be issued until every request behind completed, this should give the same effect. Am I missed something? Just to notice, @drain_next is in @ctx, so it's preserved across multiple io_enter_uring(). > -- > BR, Jackie Liu > -- Pavel Begunkov
