On 10/24/24 8:36 AM, Pavel Begunkov wrote: > On 10/23/24 17:07, Jens Axboe wrote: >> Hi, >> >> Normally a request can take a provided buffer, which means "pick a >> buffer from group X and do IO to/from it", or it can use a registered >> buffer, which means "use the buffer at index Y and do IO to/from it". >> For things like O_DIRECT and network zero copy, registered buffers can >> be used to speedup the operation, as they avoid repeated >> get_user_pages() and page referencing calls for each IO operation. >> >> Normal (non zero copy) send supports bundles, which is a way to pick >> multiple provided buffers at once and send them. send zero copy only >> supports registered buffers, and hence can only send a single buffer > > That's not true, has never been, send[msg] zc work just fine with > normal (non-registered) buffers. That's not what I'm saying, perhaps it isn't clear. What I'm trying to say is that it only supports registered buffers, it does not support provided buffers. It obviously does support regular user provided buffers that aren't registered or provided, I figured that goes without saying explicitly. >> at the time. > > And that's covered by the posted series for vectored registered > buffers support. Right, for sendmsg. >> This patchset adds support for using a mix of provided and registered >> buffers, where the provided buffers merely provide an index into which >> registered buffers to use. This enables using provided buffers for >> send zc in general, but also bundles where multiple buffers are picked. >> This is done by changing how the provided buffers are intepreted. >> Normally a provided buffer has an address, length, and buffer ID >> associated with it. The address tells the kernel where the IO should >> occur. If both fixed and provided buffers are asked for, the provided >> buffer address field is instead an encoding of the registered buffer >> index and the offset within that buffer. With that in place, using a >> combination of the two can work. > > What the series doesn't say is how it works with notifications and > what is the proposed user API in regard to it, it's the main if not > the only fundamental distinctive part of the SENDZC API. Should not change that? You'll should get the usual two notifications on send complete, and reuse safe. -- Jens Axboe
