On 2017/9/26 21:13, Wei Hu (Xavier) wrote:
On 2017/9/26 1:36, Doug Ledford wrote:
On Mon, 2017-09-25 at 20:18 +0300, Leon Romanovsky wrote:
On Mon, Sep 25, 2017 at 01:06:53PM -0400, Doug Ledford wrote:
On Wed, 2017-08-30 at 17:23 +0800, Wei Hu (Xavier) wrote:
+ /*
+ * If the command is sync, wait for the firmware to
write
back,
+ * if multi descriptors to be sent, use the first one to
check
+ */
+ if ((desc->flag) & HNS_ROCE_CMD_FLAG_NO_INTR) {
+ do {
+ if (hns_roce_cmq_csq_done(hr_dev))
+ break;
+ usleep_range(1000, 2000);
+ timeout++;
+ } while (timeout < priv->cmq.tx_timeout);
+ }
then we spin here for a maximum amount of time between 200 and
400ms,
so 1/4 to 1/2 a second. All the time we are holding the bh lock on
this CPU. That seems excessive to me. If we are going to spin
that
long, can you find a way to allocate/reserve your resources, send
the
command, then drop the bh lock while you spin, and retake it before
you
complete once the spinning is done?
They don't allocate anything in this loop, but checking the pointers
are
the same, see hns_roce_cmq_csq_done.
I'm not sure I understand your intended implication of your comment. I
wasn't concerned about them allocating anything, only that if the
hardware is hung, then this loop will hang out for 1/4 to 1/2 a second
and hold up all bottom half processing on this CPU in the meantime.
That's the sort of things that provides poor overall system behavior.
Now, since they are really only checking to see if the hardware has
gotten around to their particular command, and their command is part of
a ring structure, it's possible to record the original head command,
and our new head command, and then release the spin_lock_bh around the
entire do{ }while construct, and in hns_roce_cmd_csq_done() you could
check that head is not in the range old_head:new_head. That would
protect you in case something in the bottom half processing queued up
some more commands and from one sleep to the next the head jumped from
something other than the new_head to something past new_head, so that
head == priv->cmq.csq.next_to_use ends up being perpetually false.
But, that's just from a quick read of the code, I could easily be
missing something here...
Hi, Doug
Driver issues the cmds in cmq, and firmware gets and processes them.
The firmware process only one cmd at the same time, and it will take
about serveral to 200 us in one cmd currently, so the driver need
not to use stream mode to issue cmd.
Regards
Wei Hu
Hi, Doug
We can replace usleep_range(1000, 2000); with the following statement:
udelay(1);
to avoid spinning too long time and using usleep_range function in
spin_lock_bh locked region.
Can you give some suggestions?
Regards
Wei Hu
+#define HNS_ROCE_CMQ_TX_TIMEOUT 200
or you could reduce the size of this define...
--
Doug Ledford <dledford@xxxxxxxxxx>
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