Re: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6

[Alan Stern <stern@rowland.harvard.edu>]

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On Mon, 4 Nov 2019, Andrea Vai wrote:

> > The "linux" directory is the one generated by a fresh git clone:
> > 
> > git clone
> > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > 
> > What am I doing wrong?
> > 
> 
> Meanwhile, Alan tried to help me and gave me another patch (attached),
> which doesn't work too, but gives a different error: "The git diff
> header does not contain information about the file once removed 1
> initial component of the path (row 14)" (actually, this is my
> translation from the original message in Italian: "error:
> l'intestazione git diff non riporta le informazioni sul file una volta
> rimosso 1 componente iniziale del percorso (riga 14)")
> 
> I tested the two patches after a fresh git clone today, a few minutes
> ago.
> 
> What can I do?

You should be able to do something like this:

	cd linux
	patch -p1 </path/to/patch2

and that should work with no errors.  You don't need to use git to 
apply a patch.

In case that patch2 file was mangled somewhere along the way, I have 
attached a copy to this message.

Alan Stern

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From: Hannes Reinecke <hare@suse.com>

A scheduler might be attached even for devices exposing more than
one hardware queue, so the check for the number of hardware queue
is pointless and should be removed.

Signed-off-by: Hannes Reinecke <hare@suse.com>
---
 block/blk-mq.c |    7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 44ff3c1442a4..faab542e4836 100644
Index: usb-devel/block/blk-mq.c
===================================================================
--- usb-devel.orig/block/blk-mq.c
+++ usb-devel/block/blk-mq.c
@@ -1946,7 +1946,6 @@ static void blk_add_rq_to_plug(struct bl
 
 static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 {
-	const int is_sync = op_is_sync(bio->bi_opf);
 	const int is_flush_fua = op_is_flush(bio->bi_opf);
 	struct blk_mq_alloc_data data = { .flags = 0};
 	struct request *rq;
@@ -1992,8 +1991,7 @@ static blk_qc_t blk_mq_make_request(stru
 		/* bypass scheduler for flush rq */
 		blk_insert_flush(rq);
 		blk_mq_run_hw_queue(data.hctx, true);
-	} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs ||
-				!blk_queue_nonrot(q))) {
+	} else if (plug && (q->mq_ops->commit_rqs || !blk_queue_nonrot(q))) {
 		/*
 		 * Use plugging if we have a ->commit_rqs() hook as well, as
 		 * we know the driver uses bd->last in a smart fashion.
@@ -2041,9 +2039,6 @@ static blk_qc_t blk_mq_make_request(stru
 			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
 					&cookie);
 		}
-	} else if ((q->nr_hw_queues > 1 && is_sync) ||
-			!data.hctx->dispatch_busy) {
-		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
 	} else {
 		blk_mq_sched_insert_request(rq, false, true, true);
 	}