1. 13 Nov, 2017 5 commits
  2. 12 Nov, 2017 1 commit
    • David Howells's avatar
      timers: Add a function to start/reduce a timer · b24591e2
      David Howells authored
      
      
      Add a function, similar to mod_timer(), that will start a timer if it isn't
      running and will modify it if it is running and has an expiry time longer
      than the new time.  If the timer is running with an expiry time that's the
      same or sooner, no change is made.
      
      The function looks like:
      
      	int timer_reduce(struct timer_list *timer, unsigned long expires);
      
      This can be used by code such as networking code to make it easier to share
      a timer for multiple timeouts.  For instance, in upcoming AF_RXRPC code,
      the rxrpc_call struct will maintain a number of timeouts:
      
      	unsigned long	ack_at;
      	unsigned long	resend_at;
      	unsigned long	ping_at;
      	unsigned long	expect_rx_by;
      	unsigned long	expect_req_by;
      	unsigned long	expect_term_by;
      
      each of which is set independently of the others.  With timer reduction
      available, when the code needs to set one of the timeouts, it only needs to
      look at that timeout and then call timer_reduce() to modify the timer,
      starting it or bringing it forward if necessary.  There is no need to refer
      to the other timeouts to see which is earliest and no need to take any lock
      other than, potentially, the timer lock inside timer_reduce().
      
      Note, that this does not protect against concurrent invocations of any of
      the timer functions.
      
      As an example, the expect_rx_by timeout above, which terminates a call if
      we don't get a packet from the server within a certain time window, would
      be set something like this:
      
      	unsigned long now = jiffies;
      	unsigned long expect_rx_by = now + packet_receive_timeout;
      	WRITE_ONCE(call->expect_rx_by, expect_rx_by);
      	timer_reduce(&call->timer, expect_rx_by);
      
      The timer service code (which might, say, be in a work function) would then
      check all the timeouts to see which, if any, had triggered, deal with
      those:
      
      	t = READ_ONCE(call->ack_at);
      	if (time_after_eq(now, t)) {
      		cmpxchg(&call->ack_at, t, now + MAX_JIFFY_OFFSET);
      		set_bit(RXRPC_CALL_EV_ACK, &call->events);
      	}
      
      and then restart the timer if necessary by finding the soonest timeout that
      hasn't yet passed and then calling timer_reduce().
      
      The disadvantage of doing things this way rather than comparing the timers
      each time and calling mod_timer() is that you *will* take timer events
      unless you can finish what you're doing and delete the timer in time.
      
      The advantage of doing things this way is that you don't need to use a lock
      to work out when the next timer should be set, other than the timer's own
      lock - which you might not have to take.
      
      [ tglx: Fixed weird formatting and adopted it to pending changes ]
      
      Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: keyrings@vger.kernel.org
      Cc: linux-afs@lists.infradead.org
      Link: https://lkml.kernel.org/r/151023090769.23050.1801643667223880753.stgit@warthog.procyon.org.uk
      b24591e2
  3. 11 Nov, 2017 14 commits
  4. 10 Nov, 2017 3 commits
  5. 08 Nov, 2017 17 commits