Re: [Libguestfs] [nbdkit PATCH] cache: Reduce use of bounce-buffer

Although the time spent in memcpy/memset probably pales in comparison to time spent in socket I/O, it's still worth worth reducing the number of times we have to utilize a bounce buffer when we already have aligned data. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- filters/cache/cache.c | 60 ++++++++++++++++++++++++++++--------------- 1 file changed, 39 insertions(+), 21 deletions(-) diff --git a/filters/cache/cache.c b/filters/cache/cache.c index 19ce555..98786b5 100644 --- a/filters/cache/cache.c +++ b/filters/cache/cache.c @@ -1,5 +1,5 @@ /* nbdkit - * Copyright (C) 2018 Red Hat Inc. + * Copyright (C) 2018-2019 Red Hat Inc. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are @@ -58,6 +58,7 @@ #include "cache.h" #include "blk.h" #include "reclaim.h" +#include "isaligned.h" #define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL @@ -233,11 +234,13 @@ cache_pread (struct nbdkit_next_ops *next_ops, void *nxdata, CLEANUP_FREE uint8_t *block = NULL; assert (!flags); - block = malloc (blksize); - if (block == NULL) { - *err = errno; - nbdkit_error ("malloc: %m"); - return -1; + if (!IS_ALIGNED (count | offset, blksize)) { + block = malloc (blksize); + if (block == NULL) { + *err = errno; + nbdkit_error ("malloc: %m"); + return -1; + } } /* XXX This breaks up large read requests into smaller ones, which @@ -258,12 +261,14 @@ cache_pread (struct nbdkit_next_ops *next_ops, void *nxdata, { ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&lock); - r = blk_read (next_ops, nxdata, blknum, block, err); + r = blk_read (next_ops, nxdata, blknum, + blkoffs || n < blksize ? block : buf, err); } if (r == -1) return -1; - memcpy (buf, &block[blkoffs], n); + if (blkoffs || n < blksize) + memcpy (buf, &block[blkoffs], n);