| Message ID | 20190308025823.24382-5-lsahlber@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | cifs: simplify handling of credits for compounds | expand |
чт, 7 мар. 2019 г. в 19:35, Ronnie Sahlberg <lsahlber@redhat.com>: > > Reserve the last MAX_COMPOUND credits for any request asking for >1 credit. > This is to prevent future compound requests from becoming starved while waiting > for potentially many requests is there is a large number of concurrent > singe-credit requests. > > However, we need to protect from servers that are very slow to hand out > new credits on new sessions so we only do this IFF there are 2*MAX_COMPOUND > (arbitrary) credits already in flight. > > Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com> > --- > fs/cifs/transport.c | 28 ++++++++++++++++++++++++++++ > 1 file changed, 28 insertions(+) > > diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c > index baf15194aa3d..f4ec9635dab2 100644 > --- a/fs/cifs/transport.c > +++ b/fs/cifs/transport.c > @@ -520,6 +520,34 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits, > } > > /* > + * For normal commands, reserve the last MAX_COMPOUND > + * credits to compound requests. > + * Otherwise these compounds could be permanently > + * starved for credits by single-credit requests. > + * > + * To prevent spinning CPU, block this thread until > + * there are >MAX_COMPOUND credits available. > + * But only do this is we already have a lot of > + * credits in flight to avoid triggering this check > + * for servers that are slow to hand out credits on > + * new sessions. > + */ > + if (!optype && num_credits == 1 && > + server->in_flight > 2 * MAX_COMPOUND && > + *credits <= MAX_COMPOUND) { > + spin_unlock(&server->req_lock); > + cifs_num_waiters_inc(server); > + rc = wait_event_killable(server->request_q, > + has_credits(server, credits, > + MAX_COMPOUND + 1)); > + cifs_num_waiters_dec(server); > + if (rc) > + return rc; > + spin_lock(&server->req_lock); > + continue; > + } > + > + /* > * Can not count locking commands against total > * as they are allowed to block on server. > */ > -- > 2.13.6 > We need to watch how the the approach above work in real workloads but it looks promising. Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com> -- Best regards, Pavel Shilovsky
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c index baf15194aa3d..f4ec9635dab2 100644 --- a/fs/cifs/transport.c +++ b/fs/cifs/transport.c @@ -520,6 +520,34 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits, } /* + * For normal commands, reserve the last MAX_COMPOUND + * credits to compound requests. + * Otherwise these compounds could be permanently + * starved for credits by single-credit requests. + * + * To prevent spinning CPU, block this thread until + * there are >MAX_COMPOUND credits available. + * But only do this is we already have a lot of + * credits in flight to avoid triggering this check + * for servers that are slow to hand out credits on + * new sessions. + */ + if (!optype && num_credits == 1 && + server->in_flight > 2 * MAX_COMPOUND && + *credits <= MAX_COMPOUND) { + spin_unlock(&server->req_lock); + cifs_num_waiters_inc(server); + rc = wait_event_killable(server->request_q, + has_credits(server, credits, + MAX_COMPOUND + 1)); + cifs_num_waiters_dec(server); + if (rc) + return rc; + spin_lock(&server->req_lock); + continue; + } + + /* * Can not count locking commands against total * as they are allowed to block on server. */
Reserve the last MAX_COMPOUND credits for any request asking for >1 credit. This is to prevent future compound requests from becoming starved while waiting for potentially many requests is there is a large number of concurrent singe-credit requests. However, we need to protect from servers that are very slow to hand out new credits on new sessions so we only do this IFF there are 2*MAX_COMPOUND (arbitrary) credits already in flight. Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com> --- fs/cifs/transport.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+)