From 0c4356ba7dafc8ecb5877a42fc0d68d45ccf5951 Mon Sep 17 00:00:00 2001 From: Christian Schoenebeck Date: Wed, 29 Jul 2020 10:13:05 +0200 Subject: [PATCH] 9pfs: T_readdir latency optimization Make top half really top half and bottom half really bottom half: Each T_readdir request handling is hopping between threads (main I/O thread and background I/O driver threads) several times for every individual directory entry, which sums up to huge latencies for handling just a single T_readdir request. Instead of doing that, collect now all required directory entries (including all potentially required stat buffers for each entry) in one rush on a background I/O thread from fs driver by calling the previously added function v9fs_co_readdir_many() instead of v9fs_co_readdir(), then assemble the entire resulting network response message for the readdir request on main I/O thread. The fs driver is still aborting the directory entry retrieval loop (on the background I/O thread inside of v9fs_co_readdir_many()) as soon as it would exceed the client's requested maximum R_readdir response size. So this will not introduce a performance penalty on another end. Also: No longer seek initial directory position in v9fs_readdir(), as this is now handled (more consistently) by v9fs_co_readdir_many() instead. Signed-off-by: Christian Schoenebeck Message-Id: Signed-off-by: Christian Schoenebeck --- hw/9pfs/9p.c | 132 ++++++++++++++++++++++----------------------------- 1 file changed, 58 insertions(+), 74 deletions(-) diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c index 7a228c4828..cc4094b971 100644 --- a/hw/9pfs/9p.c +++ b/hw/9pfs/9p.c @@ -972,30 +972,6 @@ static int coroutine_fn fid_to_qid(V9fsPDU *pdu, V9fsFidState *fidp, return 0; } -static int coroutine_fn dirent_to_qid(V9fsPDU *pdu, V9fsFidState *fidp, - struct dirent *dent, V9fsQID *qidp) -{ - struct stat stbuf; - V9fsPath path; - int err; - - v9fs_path_init(&path); - - err = v9fs_co_name_to_path(pdu, &fidp->path, dent->d_name, &path); - if (err < 0) { - goto out; - } - err = v9fs_co_lstat(pdu, &path, &stbuf); - if (err < 0) { - goto out; - } - err = stat_to_qid(pdu, &stbuf, qidp); - -out: - v9fs_path_free(&path); - return err; -} - V9fsPDU *pdu_alloc(V9fsState *s) { V9fsPDU *pdu = NULL; @@ -2328,62 +2304,74 @@ size_t v9fs_readdir_response_size(V9fsString *name) return 24 + v9fs_string_size(name); } +static void v9fs_free_dirents(struct V9fsDirEnt *e) +{ + struct V9fsDirEnt *next = NULL; + + for (; e; e = next) { + next = e->next; + g_free(e->dent); + g_free(e->st); + g_free(e); + } +} + static int coroutine_fn v9fs_do_readdir(V9fsPDU *pdu, V9fsFidState *fidp, - int32_t max_count) + off_t offset, int32_t max_count) { size_t size; V9fsQID qid; V9fsString name; int len, err = 0; int32_t count = 0; - off_t saved_dir_pos; struct dirent *dent; + struct stat *st; + struct V9fsDirEnt *entries = NULL; - /* save the directory position */ - saved_dir_pos = v9fs_co_telldir(pdu, fidp); - if (saved_dir_pos < 0) { - return saved_dir_pos; + /* + * inode remapping requires the device id, which in turn might be + * different for different directory entries, so if inode remapping is + * enabled we have to make a full stat for each directory entry + */ + const bool dostat = pdu->s->ctx.export_flags & V9FS_REMAP_INODES; + + /* + * Fetch all required directory entries altogether on a background IO + * thread from fs driver. We don't want to do that for each entry + * individually, because hopping between threads (this main IO thread + * and background IO driver thread) would sum up to huge latencies. + */ + count = v9fs_co_readdir_many(pdu, fidp, &entries, offset, max_count, + dostat); + if (count < 0) { + err = count; + count = 0; + goto out; } + count = 0; - while (1) { - v9fs_readdir_lock(&fidp->fs.dir); - - err = v9fs_co_readdir(pdu, fidp, &dent); - if (err || !dent) { - break; - } - v9fs_string_init(&name); - v9fs_string_sprintf(&name, "%s", dent->d_name); - if ((count + v9fs_readdir_response_size(&name)) > max_count) { - v9fs_readdir_unlock(&fidp->fs.dir); - - /* Ran out of buffer. Set dir back to old position and return */ - v9fs_co_seekdir(pdu, fidp, saved_dir_pos); - v9fs_string_free(&name); - return count; - } + for (struct V9fsDirEnt *e = entries; e; e = e->next) { + dent = e->dent; if (pdu->s->ctx.export_flags & V9FS_REMAP_INODES) { - /* - * dirent_to_qid() implies expensive stat call for each entry, - * we must do that here though since inode remapping requires - * the device id, which in turn might be different for - * different entries; we cannot make any assumption to avoid - * that here. - */ - err = dirent_to_qid(pdu, fidp, dent, &qid); + st = e->st; + /* e->st should never be NULL, but just to be sure */ + if (!st) { + err = -1; + break; + } + + /* remap inode */ + err = stat_to_qid(pdu, st, &qid); if (err < 0) { - v9fs_readdir_unlock(&fidp->fs.dir); - v9fs_co_seekdir(pdu, fidp, saved_dir_pos); - v9fs_string_free(&name); - return err; + break; } } else { /* * Fill up just the path field of qid because the client uses * only that. To fill the entire qid structure we will have * to stat each dirent found, which is expensive. For the - * latter reason we don't call dirent_to_qid() here. Only drawback + * latter reason we don't call stat_to_qid() here. Only drawback * is that no multi-device export detection of stat_to_qid() * would be done and provided as error to the user here. But * user would get that error anyway when accessing those @@ -2396,25 +2384,26 @@ static int coroutine_fn v9fs_do_readdir(V9fsPDU *pdu, V9fsFidState *fidp, qid.version = 0; } + v9fs_string_init(&name); + v9fs_string_sprintf(&name, "%s", dent->d_name); + /* 11 = 7 + 4 (7 = start offset, 4 = space for storing count) */ len = pdu_marshal(pdu, 11 + count, "Qqbs", &qid, dent->d_off, dent->d_type, &name); - v9fs_readdir_unlock(&fidp->fs.dir); + v9fs_string_free(&name); if (len < 0) { - v9fs_co_seekdir(pdu, fidp, saved_dir_pos); - v9fs_string_free(&name); - return len; + err = len; + break; } + count += len; - v9fs_string_free(&name); - saved_dir_pos = dent->d_off; } - v9fs_readdir_unlock(&fidp->fs.dir); - +out: + v9fs_free_dirents(entries); if (err < 0) { return err; } @@ -2457,12 +2446,7 @@ static void coroutine_fn v9fs_readdir(void *opaque) retval = -EINVAL; goto out; } - if (initial_offset == 0) { - v9fs_co_rewinddir(pdu, fidp); - } else { - v9fs_co_seekdir(pdu, fidp, initial_offset); - } - count = v9fs_do_readdir(pdu, fidp, max_count); + count = v9fs_do_readdir(pdu, fidp, (off_t) initial_offset, max_count); if (count < 0) { retval = count; goto out;