From: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
To: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: BLK_QC_T_NONE and polled I/O
Date: Mon, 6 Apr 2020 11:30:23 -0700 [thread overview]
Message-ID: <44e755b7-df5c-add6-900e-25e3df63b2c6@oracle.com> (raw)
I have a question BLK_QC_T_NONE interaction with polled I/O.
Given that blk_poll() returns immediately in case of
blk_qc_t_valid(cookie), the following cases return BLK_QC_T_NONE which
seem like they would be problematic with polling:
generic_make_request()
...
if (current->bio_list) {
bio_list_add(¤t->bio_list[0], bio);
goto out; >>> this will return BLK_QC_T_NONE
}
In this case the request is deferred but should get a cookie
eventually. How would the submitter poll for this request?
__blk_mq_issue_directly()
...
case BLK_STS_RESOURCE:
case BLK_STS_DEV_RESOURCE:
blk_mq_update_dispatch_busy(hctx, true);
__blk_mq_requeue_request(rq);
break;
In this case, cookie is not updated and would keep its default
BLK_QC_T_NONE value from blk_mq_make_request(). However,
__blk_mq_requeue_request() will release the original cookie and this
request will eventually be resubmitted, so how would the submitter poll
for the completion of this request?
blk_mq_try_issue_directly()
...
ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true);
if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
blk_mq_request_bypass_insert(rq, false, true);
Incidentally, I don't see BLK_QC_T_EAGAIN used anywhere, should it be?
Thanks.
--bijan
reply other threads:[~2020-04-06 18:30 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=44e755b7-df5c-add6-900e-25e3df63b2c6@oracle.com \
--to=bijan.mottahedeh@oracle.com \
--cc=linux-block@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).