linux-ext4 - Re: [RFCv3 10/10] iomap: Add trace points for DIO path

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Date:   Fri, 14 Apr 2023 20:08:55 +0530
From:   Ritesh Harjani (IBM) <ritesh.list@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        Jan Kara <jack@...e.cz>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
        Disha Goel <disgoel@...ux.ibm.com>
Subject: Re: [RFCv3 10/10] iomap: Add trace points for DIO path

Christoph Hellwig <hch@...radead.org> writes:

> On Fri, Apr 14, 2023 at 01:26:38PM +0530, Ritesh Harjani wrote:
>> How about this below change? Does this look good to you?
>> It should cover all error types and both entry and exit.
>
> I don't think it is very useful.  The complete tracepoint is the
> end of the I/O.  Having a separate end one doesn't make sense.
> That's why I suggested a queued one for the asynchronous case.

Ok, does this look good then?

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 36ab1152dbea..859efb5de1bf 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -130,6 +130,7 @@ ssize_t iomap_dio_complete(struct iomap_dio *dio)
        if (ret > 0)
                ret += dio->done_before;

+       trace_iomap_dio_complete(iocb, dio->error, ret);
        kfree(dio);

        return ret;
@@ -650,8 +651,12 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
         */
        dio->wait_for_completion = wait_for_completion;
        if (!atomic_dec_and_test(&dio->ref)) {
-               if (!wait_for_completion)
-                       return ERR_PTR(-EIOCBQUEUED);
+               if (!wait_for_completion) {
+                       ret = -EIOCBQUEUED;
+                       trace_iomap_dio_rw_queued(iocb, iter, dio_flags,
+                                                 done_before, ret);
+                       return ERR_PTR(ret);
+               }

                for (;;) {
                        set_current_state(TASK_UNINTERRUPTIBLE);

-ritesh