On 3/8/23 01:08, Ming Lei wrote:
On Tue, Mar 07, 2023 at 03:37:21PM +0000, Pavel Begunkov wrote:
On 3/7/23 14:15, Ming Lei wrote:
Hello,
Add IORING_OP_FUSED_CMD, it is one special URING_CMD, which has to
be SQE128. The 1st SQE(master) is one 64byte URING_CMD, and the 2nd
64byte SQE(slave) is another normal 64byte OP. For any OP which needs
to support slave OP, io_issue_defs[op].fused_slave needs to be set as 1,
and its ->issue() can retrieve/import buffer from master request's
fused_cmd_kbuf. The slave OP is actually submitted from kernel, part of
this idea is from Xiaoguang's ublk ebpf patchset, but this patchset
submits slave OP just like normal OP issued from userspace, that said,
SQE order is kept, and batching handling is done too.
From a quick look through patches it all looks a bit complicated
and intrusive, all over generic hot paths. I think instead we
Really? The main change to generic hot paths are adding one 'true/false'
parameter to io_init_req(). For others, the change is just check on
req->flags or issue_flags, which is basically zero cost.
Extra flag in io_init_req() but also exporting it, which is an
internal function, to non-core code. Additionally it un-inlines it
and even looks recurse calls it (max depth 2). From a quick look,
there is some hand coded ->cached_refs manipulations, it takes extra
space in generic sections of io_kiocb. It makes all cmd users to
check for IO_URING_F_FUSED. There is also a two-way dependency b/w
requests, which never plays out well, e.g. I still hate how linked
timeouts stick out in generic paths.
Depending on SQE128 also doesn't seem right, though it can be dealt
with, e.g. sth like how it's done with links requests.
should be able to use registered buffer table as intermediary and
reuse splicing. Let me try it out
I will take a look at you patch, but last time, Linus has pointed out that
splice isn't one good way, in which buffer ownership transferring is one big
issue for writing data to page retrieved from pipe.
There are no real pipes, better to say io_uring replaces a pipe,
and splice bits are used to get pages from a file. Though, there
will be some common problems. Thanks for the link, I'll need to
get through it first, thanks for the link
https://lore.kernel.org/linux-block/CAJfpeguQ3xn2-6svkkVXJ88tiVfcDd-eKi1evzzfvu305fMoyw@xxxxxxxxxxxxxx/
--
Pavel Begunkov
