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Date:      Tue, 17 Dec 2019 00:13:45 +0000 (UTC)
From:      Warner Losh <imp@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r355837 - head/sys/cam
Message-ID:  <201912170013.xBH0DjZY090730@repo.freebsd.org>

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Author: imp
Date: Tue Dec 17 00:13:45 2019
New Revision: 355837
URL: https://svnweb.freebsd.org/changeset/base/355837

Log:
  Implement bio_speedup
  
  React to the BIO_SPEED command in the cam io scheduler by completing
  as successful BIO_DELETE commands that are pending, up to the length
  passed down in the BIO_SPEEDUP cmomand. The length passed down is a
  hint for how much space on the drive needs to be recovered. By
  completing the BIO_DELETE comomands, this allows the upper layers to
  allocate and write to the blocks that were about to be trimmed. Since
  FreeBSD implements TRIMSs as advisory, we can eliminliminate them and
  go directly to writing.
  
  The biggest benefit from TRIMS coomes ffrom the drive being able t
  ooptimize its free block pool inthe log run. There's little nto no
  bene3efit in the shoort term. , sepeciall whn the trim is followed by
  a write. Speedup lets  us make this tradeoff.
  
  Reviewed by: kirk, kib
  Sponsored by: Netflix
  Differential Revision: https://reviews.freebsd.org/D18351

Modified:
  head/sys/cam/cam_iosched.c

Modified: head/sys/cam/cam_iosched.c
==============================================================================
--- head/sys/cam/cam_iosched.c	Tue Dec 17 00:13:40 2019	(r355836)
+++ head/sys/cam/cam_iosched.c	Tue Dec 17 00:13:45 2019	(r355837)
@@ -1534,6 +1534,41 @@ cam_iosched_queue_work(struct cam_iosched_softc *isc, 
 {
 
 	/*
+	 * A BIO_SPEEDUP from the uppper layers means that they have a block
+	 * shortage. At the present, this is only sent when we're trying to
+	 * allocate blocks, but have a shortage before giving up. bio_length is
+	 * the size of their shortage. We will complete just enough BIO_DELETEs
+	 * in the queue to satisfy the need. If bio_length is 0, we'll complete
+	 * them all. This allows the scheduler to delay BIO_DELETEs to improve
+	 * read/write performance without worrying about the upper layers. When
+	 * it's possibly a problem, we respond by pretending the BIO_DELETEs
+	 * just worked. We can't do anything about the BIO_DELETEs in the
+	 * hardware, though. We have to wait for them to complete.
+	 */
+	if (bp->bio_cmd == BIO_SPEEDUP) {
+		off_t len;
+		struct bio *nbp;
+
+		len = 0;
+		while (bioq_first(&isc->trim_queue) &&
+		    (bp->bio_length == 0 || len < bp->bio_length)) {
+			nbp = bioq_takefirst(&isc->trim_queue);
+			len += nbp->bio_length;
+			nbp->bio_error = 0;
+			biodone(nbp);
+		}
+		if (bp->bio_length > 0) {
+			if (bp->bio_length > len)
+				bp->bio_resid = bp->bio_length - len;
+			else
+				bp->bio_resid = 0;
+		}
+		bp->bio_error = 0;
+		biodone(bp);
+		return;
+	}
+
+	/*
 	 * If we get a BIO_FLUSH, and we're doing delayed BIO_DELETEs then we
 	 * set the last tick time to one less than the current ticks minus the
 	 * delay to force the BIO_DELETEs to be presented to the client driver.
@@ -1919,8 +1954,8 @@ DB_SHOW_COMMAND(iosched, cam_iosched_db_show)
 	db_printf("Trim Q len         %d\n", biolen(&isc->trim_queue));
 	db_printf("read_bias:         %d\n", isc->read_bias);
 	db_printf("current_read_bias: %d\n", isc->current_read_bias);
-	db_printf("Trims active       %d\n", isc->pend_trim);
-	db_printf("Max trims active   %d\n", isc->max_trim);
+	db_printf("Trims active       %d\n", isc->pend_trims);
+	db_printf("Max trims active   %d\n", isc->max_trims);
 }
 #endif
 #endif



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