Content-Type: multipart/mixed; boundary="===============4309473970205684450==" MIME-Version: 1.0 From: NeilBrown To: lkp@lists.01.org Subject: [PATCH] locks: fix performance regressions. Date: Wed, 28 Nov 2018 11:53:48 +1100 Message-ID: <87k1kyowdf.fsf@notabene.neil.brown.name> In-Reply-To: <87mupup0ot.fsf@notabene.neil.brown.name> List-Id: --===============4309473970205684450== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable The kernel test robot reported two performance regressions caused by recent patches. Both appear to related to the global spinlock blocked_lock_lock being taken more often. This patch avoids taking that lock in the cases tested. Reported-by: kernel test robot Signed-off-by: NeilBrown --- Hi Jeff, you might like to merge these back into the patches that introduced the problem. Or you might like me to re-send the series with these merged in, in which case, please ask. And a BIG thank-you to the kernel-test-robot team!! Thanks, NeilBrown fs/locks.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/fs/locks.c b/fs/locks.c index f456cd3d9d50..67519a43e27a 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -444,6 +444,13 @@ static void locks_move_blocks(struct file_lock *new, s= truct file_lock *fl) { struct file_lock *f; = + /* + * As ctx->flc_lock is held, new requests cannot be added to + * ->fl_blocked_requests, so we don't need a lock to check if it + * is empty. + */ + if (list_empty(&fl->fl_blocked_requests)) + return; spin_lock(&blocked_lock_lock); list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests); list_for_each_entry(f, &fl->fl_blocked_requests, fl_blocked_member) @@ -749,6 +756,20 @@ int locks_delete_block(struct file_lock *waiter) { int status =3D -ENOENT; = + /* + * If fl_blocker is NULL, it won't be set again as this thread + * "owns" the lock and is the only one that might try to claim + * the lock. So it is safe to test fl_blocker locklessly. + * Also if fl_blocker is NULL, this waiter is not listed on + * fl_blocked_requests for some lock, so no other request can + * be added to the list of fl_blocked_requests for this + * request. So if fl_blocker is NULL, it is safe to + * locklessly check if fl_blocked_requests is empty. If both + * of these checks succeed, there is no need to take the lock. + */ + if (waiter->fl_blocker =3D=3D NULL && + list_empty(&waiter->fl_blocked_requests)) + return status; spin_lock(&blocked_lock_lock); if (waiter->fl_blocker) status =3D 0; -- = 2.14.0.rc0.dirty --===============4309473970205684450== Content-Type: application/pgp-signature MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="signature.asc" LS0tLS1CRUdJTiBQR1AgU0lHTkFUVVJFLS0tLS0KCmlRSXpCQUVCQ0FBZEZpRUVHOFlwNjlPUTJI QjdYMGw2T2V5ZTNWWmlnYmtGQWx2OTV4d0FDZ2tRT2V5ZTNWWmkKZ2JrMGpCQUFqRENCdGZIY2Ew VzY0Y0QyU0g4V1JUbWJ3NEYwb0dWYnJTNjNnOTZ4VzhhcDZJa0tEUVlJVjJkMgpEMnlIT3l5U21B aG1RcUtoRzJzZmN6NVczTXRpYjVGaWF1elZFUzdpeitvNWNBdkJFckN6QUxmcTNCNzZtQmxZClEz TW5TR0xnZTQ2eE9wRU5zZlV4a3Vib0gvdjNmWUJJQmRCL2M3bEs0NVhVMzJjOENKNmZSWnpyQmhu OWxWSTQKRWdlMVAxcnBKaVhNQUx1Ti9Dc2MwTHI5dVg5UE83ZlFkOW12WC83OW5vVjJMMDJoenU3 Vnl0WjhYRW9YbnpGTQpvLzJnZFNMbWxTZUNpakgvdDJsb3E4QTZEUHZ1QWhLVE9IZmtPNFFOWkZM UTlONm45RWl6ZHBSaERiUXRYbGZaCmQzSHAzcDNtZjkvQnRyTmNZaU5XODVMRWJmZkxoUEg4bVdU enQ2YVQ1b3dkM1h4MEtFeFFYUWpha3I3UmoyZnAKRURYQ3BuaWx6U3VoNUlhNTVuV0dtQkFBL2hN ZUpZdEtxcDZtcEVyVmtFbEZmLzFxaDNMYkg3aXhobERKdStzcApBbU9RbStFMjZWOG5iVFVXc3Q0 ajh3SUVxL3V4NHV6a1JHbExxTEdIYkEwVDlUWmx5c2xHQnJJbDQvZWRKYlp6Cit1Y0Zyamx6eTFS U203UDg2VXZ6VjFzMGNBZ2g5VlM4WXRvNS9PdTI2WlhySElmK0lqbkFLUHRGMXE3bGIrY28Kc0dE eGJMdkhBQm1rVG1hTnMwTlM2REZNM1AybklPZ0ViNHBHQ2NZSThoSnR1K0tjdVRabEtSd01QNFBs QUx6YwpmcmNGT05KWWRjd2w1QWQxWlkzMmhpMnY4cS9MZm5FWDZPQTM4bi9YSnhSNUt0Rno3WVk9 Cj1SNnRvCi0tLS0tRU5EIFBHUCBTSUdOQVRVUkUtLS0tLQ== --===============4309473970205684450==--