On Thu, 8 Sep 2022 13:23:53 +0200 Linus Heckemann <g...@sphalerite.org> 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 every open, > stat, read, write, etc operation. > > 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. > > Signed-off-by: Linus Heckemann <g...@sphalerite.org> > Reviewed-by: Philippe Mathieu-Daudé <f4...@amsat.org> > Reviewed-by: Greg Kurz <gr...@kaod.org> > --- > > Greg Kurz writes: > > The comment above should be adapted to the new situation : no need > > I've removed it completely, since the logic is simple enough that only > the shortened comment below remains necessary. > > > With the new logic, this should just be: > > now is :) > > > g_hash_table_steal_extended() [1] actually allows to do just that. > > g_hash_table_steal_extended unfortunately isn't available since it was > introduced in glib 2.58 and we're maintaining compatibility to 2.56. > Ha... this could be addressed through conditional compilation, e.g.: static V9fsFidState *clunk_fid(V9fsState *s, int32_t fid) { V9fsFidState *fidp; #if GLIB_CHECK_VERSION(2,56,0) if (!g_hash_table_steal_extended(s->fids, GINT_TO_POINTER(fid), NULL, (gpointer *) &fidp)) { return NULL; } #else fidp = g_hash_table_lookup(s->fids, GINT_TO_POINTER(fid)); if (fidp) { g_hash_table_remove(s->fids, GINT_TO_POINTER(fid)); } else { return NULL; } #endif fidp->clunked = true; return fidp; } or simply leave a TODO comment so that we don't forget. > > You could just call g_hash_table_iter_remove(&iter) here > > Applied this suggestion, thanks! > > > > Well... finding at least one clunked fid state in this table is > > definitely a bug so I'll keep the BUG_ON() anyway. > > Christian Schoenebeck writes: > > Yeah, I think you are right, it would feel odd. Just drop BUG_ON() for > > now. > > I still prefer dropping it, but if we were to keep it I think it should > be in v9fs_reclaim_fd where we iterate and can thus check the whole > table. > IMO the relevant aspect isn't really about checking the whole table, but rather not to get a clunked fid out of this table and pass it over. > > Greg Kurz and Philippe Mathieu-Daudé write: > > [patch versioning] > > Whoops. I used -v2 on git send-email, which just ignored the option, > rather than git format-patch, by accident. This one _should_ now be v3! > > v3 it is and LGTM ! No big deal with the BUG_ON(), given the improvement. My R-b stands. Thanks Linus ! > hw/9pfs/9p.c | 140 +++++++++++++++++++++++++-------------------------- > hw/9pfs/9p.h | 2 +- > 2 files changed, 70 insertions(+), 72 deletions(-) > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c > index aebadeaa03..98a475e560 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; > } > 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; > } > 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, (gpointer *) &f)) { > /* > * Unlink fids cannot be reclaimed. Check > * for them and skip them. Also skip fids > @@ -518,23 +517,19 @@ 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; > > - fidp = QSIMPLEQ_FIRST(&s->fid_list); > - if (!fidp) { > - return 0; > - } > + g_hash_table_iter_init(&iter, s->fids); > + > + while (g_hash_table_iter_next(&iter, &fid, (gpointer *) &fidp)) { > + /* > + * Ensure the fid survives a potential clunk request during > + * v9fs_reopen_fid. > + */ > + fidp->ref++; > > - /* > - * v9fs_reopen_fid() can yield : a reference on the fid must be held > - * to ensure its pointer remains valid and we can safely pass it to > - * QSIMPLEQ_NEXT(). The corresponding put_fid() can also yield so > - * we must keep a reference on the next fid as well. So the logic here > - * is to get a reference on a fid and only put it back during the next > - * iteration after we could get a reference on the next fid. Start with > - * the first one. > - */ > - for (fidp->ref++; fidp; fidp = fidp_next) { > if (fidp->path.size == path->size && > !memcmp(fidp->path.data, path->data, path->size)) { > /* Mark the fid non reclaimable. */ > @@ -548,16 +543,6 @@ 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); > } > @@ -569,18 +554,20 @@ 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, (gpointer *) &fidp)) { > fidp->ref++; > > /* Clunk fid */ > - QSIMPLEQ_REMOVE(&s->fid_list, fidp, V9fsFidState, next); > fidp->clunked = true; > > put_fid(pdu, fidp); > + g_hash_table_iter_remove(&iter); > } > } > > @@ -3205,6 +3192,8 @@ static int coroutine_fn v9fs_complete_rename(V9fsPDU > *pdu, V9fsFidState *fidp, > V9fsFidState *tfidp; > V9fsState *s = pdu->s; > V9fsFidState *dirfidp = NULL; > + GHashTableIter iter; > + gpointer fid; > > v9fs_path_init(&new_path); > if (newdirfid != -1) { > @@ -3238,11 +3227,13 @@ 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, (gpointer *) &tfidp)) { > if (v9fs_path_is_ancestor(&fidp->path, &tfidp->path)) { > /* replace the name */ > v9fs_fix_path(&tfidp->path, &new_path, strlen(fidp->path.data)); > @@ -3320,6 +3311,8 @@ static int coroutine_fn v9fs_fix_fid_paths(V9fsPDU > *pdu, V9fsPath *olddir, > V9fsPath oldpath, newpath; > V9fsState *s = pdu->s; > int err; > + GHashTableIter iter; > + gpointer fid; > > v9fs_path_init(&oldpath); > v9fs_path_init(&newpath); > @@ -3336,7 +3329,8 @@ 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, (gpointer *) &tfidp)) { > if (v9fs_path_is_ancestor(&oldpath, &tfidp->path)) { > /* replace the name */ > v9fs_fix_path(&tfidp->path, &newpath, strlen(oldpath.data)); > @@ -4226,7 +4220,7 @@ 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) { > @@ -4286,6 +4280,10 @@ void v9fs_device_unrealize_common(V9fsState *s) > if (s->ctx.fst) { > fsdev_throttle_cleanup(s->ctx.fst); > } > + if (s->fids) { > + g_hash_table_destroy(s->fids); > + s->fids = NULL; > + } > g_free(s->tag); > qp_table_destroy(&s->qpd_table); > qp_table_destroy(&s->qpp_table); > 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;