On Samstag, 3. September 2022 17:03:27 CEST Linus Heckemann wrote: > The previous implementation would iterate over the fid table for > lookup operations, resulting in an operation with O(n) complexity on > the number of open files and poor cache locality -- for nearly every > open, stat, read, write, etc operation.
Oh yes, I had this on my TODO list for a long time. Thanks for the effort Linus! > This change uses a hashtable for this instead, significantly improving > the performance of the 9p filesystem. The runtime of NixOS's simple > installer test, which copies ~122k files totalling ~1.8GiB from 9p, > decreased by a factor of about 10. Wow, even more than I expected. Nice! I have a feeling that this will also fix the massive slow downs that were seen after running for a long time. Because I think that slow down was because a large amount of fids were accumulated over time, where this O(n) issue hurts more noticably. Some remarks below ... > Signed-off-by: Linus Heckemann <g...@sphalerite.org> > --- > hw/9pfs/9p.c | 130 +++++++++++++++++++++++++++------------------------ > hw/9pfs/9p.h | 2 +- > 2 files changed, 69 insertions(+), 63 deletions(-) > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c > index aebadeaa03..ff466afe39 100644 > --- a/hw/9pfs/9p.c > +++ b/hw/9pfs/9p.c > @@ -282,33 +282,31 @@ static V9fsFidState *coroutine_fn get_fid(V9fsPDU > *pdu, int32_t fid) V9fsFidState *f; > V9fsState *s = pdu->s; > > - QSIMPLEQ_FOREACH(f, &s->fid_list, next) { > - BUG_ON(f->clunked); > - if (f->fid == fid) { > - /* > - * Update the fid ref upfront so that > - * we don't get reclaimed when we yield > - * in open later. > - */ > - f->ref++; > - /* > - * check whether we need to reopen the > - * file. We might have closed the fd > - * while trying to free up some file > - * descriptors. > - */ > - err = v9fs_reopen_fid(pdu, f); > - if (err < 0) { > - f->ref--; > - return NULL; > - } > - /* > - * Mark the fid as referenced so that the LRU > - * reclaim won't close the file descriptor > - */ > - f->flags |= FID_REFERENCED; > - return f; > + f = g_hash_table_lookup(s->fids, GINT_TO_POINTER(fid)); > + if (f) { > + /* > + * Update the fid ref upfront so that > + * we don't get reclaimed when we yield > + * in open later. > + */ > + f->ref++; > + /* > + * check whether we need to reopen the > + * file. We might have closed the fd > + * while trying to free up some file > + * descriptors. > + */ > + err = v9fs_reopen_fid(pdu, f); > + if (err < 0) { > + f->ref--; > + return NULL; > } > + /* > + * Mark the fid as referenced so that the LRU > + * reclaim won't close the file descriptor > + */ > + f->flags |= FID_REFERENCED; > + return f; > } > return NULL; > } > @@ -317,12 +315,9 @@ static V9fsFidState *alloc_fid(V9fsState *s, int32_t > fid) { > V9fsFidState *f; > > - QSIMPLEQ_FOREACH(f, &s->fid_list, next) { > + if (g_hash_table_contains(s->fids, GINT_TO_POINTER(fid))) { > /* If fid is already there return NULL */ > - BUG_ON(f->clunked); > - if (f->fid == fid) { > - return NULL; > - } > + return NULL; Probably retaining BUG_ON(f->clunked) here? > } > f = g_new0(V9fsFidState, 1); > f->fid = fid; > @@ -333,7 +328,7 @@ static V9fsFidState *alloc_fid(V9fsState *s, int32_t > fid) * reclaim won't close the file descriptor > */ > f->flags |= FID_REFERENCED; > - QSIMPLEQ_INSERT_TAIL(&s->fid_list, f, next); > + g_hash_table_insert(s->fids, GINT_TO_POINTER(fid), f); > > v9fs_readdir_init(s->proto_version, &f->fs.dir); > v9fs_readdir_init(s->proto_version, &f->fs_reclaim.dir); > @@ -424,12 +419,11 @@ static V9fsFidState *clunk_fid(V9fsState *s, int32_t > fid) { > V9fsFidState *fidp; > > - QSIMPLEQ_FOREACH(fidp, &s->fid_list, next) { > - if (fidp->fid == fid) { > - QSIMPLEQ_REMOVE(&s->fid_list, fidp, V9fsFidState, next); > - fidp->clunked = true; > - return fidp; > - } > + fidp = g_hash_table_lookup(s->fids, GINT_TO_POINTER(fid)); > + if (fidp) { > + g_hash_table_remove(s->fids, GINT_TO_POINTER(fid)); > + fidp->clunked = true; > + return fidp; We can't get rid of the double lookup here, can we? Surprisingly I don't find a lookup function on the iterator based API. > } > return NULL; > } > @@ -439,10 +433,15 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu) > int reclaim_count = 0; > V9fsState *s = pdu->s; > V9fsFidState *f; > + > + GHashTableIter iter; > + gpointer fid; > + g_hash_table_iter_init(&iter, s->fids); > + > QSLIST_HEAD(, V9fsFidState) reclaim_list = > QSLIST_HEAD_INITIALIZER(reclaim_list); > > - QSIMPLEQ_FOREACH(f, &s->fid_list, next) { > + while (g_hash_table_iter_next(&iter, &fid, (void **) &f)) { > /* > * Unlink fids cannot be reclaimed. Check > * for them and skip them. Also skip fids > @@ -518,12 +517,12 @@ static int coroutine_fn > v9fs_mark_fids_unreclaim(V9fsPDU *pdu, V9fsPath *path) { > int err; > V9fsState *s = pdu->s; > - V9fsFidState *fidp, *fidp_next; > + V9fsFidState *fidp; > + gpointer fid; > + > + GHashTableIter iter; > + g_hash_table_iter_init(&iter, s->fids); > > - fidp = QSIMPLEQ_FIRST(&s->fid_list); > - if (!fidp) { > - return 0; > - } > > /* > * v9fs_reopen_fid() can yield : a reference on the fid must be held > @@ -534,7 +533,13 @@ static int coroutine_fn > v9fs_mark_fids_unreclaim(V9fsPDU *pdu, V9fsPath *path) * iteration after we > could get a reference on the next fid. Start with * the first one. > */ > - for (fidp->ref++; fidp; fidp = fidp_next) { > + while (g_hash_table_iter_next(&iter, &fid, (void **) &fidp)) { Too bad that there's apparently no macro based g_hash_table_foreach(), that would have made the code a bit cleaner and shorter than using an iterator while loop, but OK. Best regards, Christian Schoenebeck > + /* > + * Ensure the fid survives a potential clunk request during > + * put_fid() below and v9fs_reopen_fid() in the next iteration. > + */ > + fidp->ref++; > + > if (fidp->path.size == path->size && > !memcmp(fidp->path.data, path->data, path->size)) { > /* Mark the fid non reclaimable. */ > @@ -548,16 +553,6 @@ static int coroutine_fn > v9fs_mark_fids_unreclaim(V9fsPDU *pdu, V9fsPath *path) } > } > > - fidp_next = QSIMPLEQ_NEXT(fidp, next); > - > - if (fidp_next) { > - /* > - * Ensure the next fid survives a potential clunk request > during - * put_fid() below and v9fs_reopen_fid() in the next > iteration. - */ > - fidp_next->ref++; > - } > - > /* We're done with this fid */ > put_fid(pdu, fidp); > } > @@ -570,18 +565,20 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu) > V9fsState *s = pdu->s; > V9fsFidState *fidp; > > + gpointer fid; > + GHashTableIter iter; > + g_hash_table_iter_init(&iter, s->fids); > + > /* Free all fids */ > - while (!QSIMPLEQ_EMPTY(&s->fid_list)) { > - /* Get fid */ > - fidp = QSIMPLEQ_FIRST(&s->fid_list); > + while (g_hash_table_iter_next(&iter, &fid, (void **) &fidp)) { > fidp->ref++; > > /* Clunk fid */ > - QSIMPLEQ_REMOVE(&s->fid_list, fidp, V9fsFidState, next); > fidp->clunked = true; > > put_fid(pdu, fidp); > } > + g_hash_table_remove_all(s->fids); > } > > #define P9_QID_TYPE_DIR 0x80 > @@ -3206,6 +3203,9 @@ static int coroutine_fn v9fs_complete_rename(V9fsPDU > *pdu, V9fsFidState *fidp, V9fsState *s = pdu->s; > V9fsFidState *dirfidp = NULL; > > + GHashTableIter iter; > + gpointer fid; > + > v9fs_path_init(&new_path); > if (newdirfid != -1) { > dirfidp = get_fid(pdu, newdirfid); > @@ -3238,11 +3238,13 @@ static int coroutine_fn v9fs_complete_rename(V9fsPDU > *pdu, V9fsFidState *fidp, if (err < 0) { > goto out; > } > + > /* > * Fixup fid's pointing to the old name to > * start pointing to the new name > */ > - QSIMPLEQ_FOREACH(tfidp, &s->fid_list, next) { > + g_hash_table_iter_init(&iter, s->fids); > + while (g_hash_table_iter_next(&iter, &fid, (void **) &tfidp)) { > if (v9fs_path_is_ancestor(&fidp->path, &tfidp->path)) { > /* replace the name */ > v9fs_fix_path(&tfidp->path, &new_path, > strlen(fidp->path.data)); @@ -3321,6 +3323,9 @@ static int coroutine_fn > v9fs_fix_fid_paths(V9fsPDU *pdu, V9fsPath *olddir, V9fsState *s = pdu->s; > int err; > > + GHashTableIter iter; > + gpointer fid; > + > v9fs_path_init(&oldpath); > v9fs_path_init(&newpath); > err = v9fs_co_name_to_path(pdu, olddir, old_name->data, &oldpath); > @@ -3336,7 +3341,8 @@ static int coroutine_fn v9fs_fix_fid_paths(V9fsPDU > *pdu, V9fsPath *olddir, * Fixup fid's pointing to the old name to > * start pointing to the new name > */ > - QSIMPLEQ_FOREACH(tfidp, &s->fid_list, next) { > + g_hash_table_iter_init(&iter, s->fids); > + while (g_hash_table_iter_next(&iter, &fid, (void **) &tfidp)) { > if (v9fs_path_is_ancestor(&oldpath, &tfidp->path)) { > /* replace the name */ > v9fs_fix_path(&tfidp->path, &newpath, strlen(oldpath.data)); > @@ -4226,7 +4232,7 @@ int v9fs_device_realize_common(V9fsState *s, const > V9fsTransport *t, s->ctx.fmode = fse->fmode; > s->ctx.dmode = fse->dmode; > > - QSIMPLEQ_INIT(&s->fid_list); > + s->fids = g_hash_table_new(NULL, NULL); > qemu_co_rwlock_init(&s->rename_lock); > > if (s->ops->init(&s->ctx, errp) < 0) { > diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h > index 994f952600..10fd2076c2 100644 > --- a/hw/9pfs/9p.h > +++ b/hw/9pfs/9p.h > @@ -339,7 +339,7 @@ typedef struct { > struct V9fsState { > QLIST_HEAD(, V9fsPDU) free_list; > QLIST_HEAD(, V9fsPDU) active_list; > - QSIMPLEQ_HEAD(, V9fsFidState) fid_list; > + GHashTable *fids; > FileOperations *ops; > FsContext ctx; > char *tag;