________________________________________ From: Caleb Sander Mateos <csander@xxxxxxxxxxxxxxx> Sent: Thursday, April 24, 2025 9:28 PM To: Ofer Oshri <ofer@xxxxxxxxxx> Cc: linux-block@xxxxxxxxxxxxxxx <linux-block@xxxxxxxxxxxxxxx>; ming.lei@xxxxxxxxxx <ming.lei@xxxxxxxxxx>; axboe@xxxxxxxxx <axboe@xxxxxxxxx>; Jared Holzman <jholzman@xxxxxxxxxx>; Yoav Cohen <yoav@xxxxxxxxxx>; Guy Eisenberg <geisenberg@xxxxxxxxxx>; Omri Levi <omril@xxxxxxxxxx> Subject: Re: ublk: RFC fetch_req_multishot External email: Use caution opening links or attachments On Thu, Apr 24, 2025 at 11:19 AM Ofer Oshri <ofer@xxxxxxxxxx> wrote: > > Hi, > > Our code uses a single io_uring per core, which is shared among all block devices - meaning each block device on a core uses the same io_uring. > > Let’s say the size of the io_uring is N. Each block device submits M UBLK_U_IO_FETCH_REQ requests. As a result, with the current implementation, we can only support up to P block devices, where P = N / M. This means that when we attempt to support block device P+1, it will fail due to io_uring exhaustion. What do you mean by "size of the io_uring", the submission queue size? Why can't you submit all P * M UBLK_U_IO_FETCH_REQ operations in batches of N? Best, Caleb N is the size of the submission queue, and P is not fixed and unknown at the time of ring initialization....
