git: 248682a58915 - main - loader bcache: Allow readahead up to 256 kB I/Os

[Colin Percival]

The branch main has been updated by cperciva:

URL: https://cgit.FreeBSD.org/src/commit/?id=248682a589159619aa5f2019e415a423e849e327

commit 248682a589159619aa5f2019e415a423e849e327
Author:     Colin Percival <cperciva at FreeBSD.org>
AuthorDate: 2021-10-03 21:55:10 +0000
Commit:     Colin Percival <cperciva at FreeBSD.org>
CommitDate: 2021-10-03 21:55:10 +0000

    loader bcache: Allow readahead up to 256 kB I/Os
    
    Prior to this commit, the loader would perform readaheads of up to
    128 kB; when booting on a UFS filesystem this resulted in a series
    of 160 kB reads (32 kB request + 128 kB readahead).
    
    This commit allows readaheads to be longer, subject to a total I/O
    size limit of 256 kB; i.e. 32 kB read requests will have added
    readaheads of up to 224 kB.
    
    In my testing on an EC2 c5.xlarge instance, this change reduces the
    boot time by roughly 80 ms.
    
    Reviewed by:    tsoome
    MFC after:      1 week
    Sponsored by:   https://www.patreon.com/cperciva
    Differential Revision:  https://reviews.freebsd.org/D32251
---
 stand/common/bcache.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/stand/common/bcache.c b/stand/common/bcache.c
index b79d609b198b..99c78b0346b7 100644
--- a/stand/common/bcache.c
+++ b/stand/common/bcache.c
@@ -86,8 +86,9 @@ static u_int bcache_rablks;
 #define	BHASH(bc, blkno)	((blkno) & ((bc)->bcache_nblks - 1))
 #define	BCACHE_LOOKUP(bc, blkno)	\
 	((bc)->bcache_ctl[BHASH((bc), (blkno))].bc_blkno != (blkno))
-#define	BCACHE_READAHEAD	256
+#define	BCACHE_READAHEAD	512
 #define	BCACHE_MINREADAHEAD	32
+#define	BCACHE_MAXIOWRA		512
 
 static void	bcache_invalidate(struct bcache *bc, daddr_t blkno);
 static void	bcache_insert(struct bcache *bc, daddr_t blkno);
@@ -324,6 +325,8 @@ read_strategy(void *devdata, int rw, daddr_t blk, size_t size,
     if (ra != 0 && ra != bc->bcache_nblks) { /* do we have RA space? */
 	ra = MIN(bc->ra, ra - 1);
 	ra = rounddown(ra, 16);		/* multiple of 16 blocks */
+	if (ra + p_size > BCACHE_MAXIOWRA)
+	    ra = BCACHE_MAXIOWRA - p_size;
 	bc->ralen = ra;
 	p_size += ra;
     } else {