On 12/07/2017 09:47, wangyijing wrote:
在 2017/7/12 16:17, John Garry 写道:
On 12/07/2017 03:06, wangyijing wrote:
- unsigned long port_events_pending;
- unsigned long phy_events_pending;
+ struct asd_sas_event port_events[PORT_POOL_SIZE];
+ struct asd_sas_event phy_events[PHY_POOL_SIZE];
int error;
Hi Yijing,
So now we are creating a static pool of events per PHY/port, instead of having
1 static work struct per event per PHY/port. So, for sure, this avoids the
dynamic event issue of system memory exhaustion which we discussed in v1+v2
series. And it seems to possibly remove issue of losing SAS events.
But how did you determine the pool size for a PHY/port? It would seem to be 5 *
#phy events or #port events (which is also 5, I figure by coincidence). How does
this deal with flutter of >25 events?
There is no special meaning for the pool size, if flutter of > 25 events,
notify sas events will return error, and the further step work is depending on
LLDD drivers.
I hope libsas could do more work in this case, but now it seems a little
difficult, this patch may be a interim fix, until we find a perfect solution.
The principal of having a fixed-sized pool is ok, even though the pool size
needs more consideration.
However my issue is how to handle pool exhaustion. For a start, relaying info to the LLDD
that the event notification failed is probably not the way to go. I only now noticed
"scsi: sas: scsi_queue_work can fail, so make callers aware" made it into the
kernel; as I mentioned in response to this patch, the LLDD does not know how to handle
this (and no LLDDs do actually handle this).
I would say it is better to shut down the PHY from libsas (As Dan mentioned in
the v1 series) when the pool exhausts, under the assumption that the PHY has
gone into some erroneous state. The user can later re-enable the PHY from
sysfs, if required.
I considered this suggestion, and what I am worried about are, first if we
disable phy once the sas event pool exhausts, it may hurt the pending sas event
process which has been queued,
I don't see how it affects currently queued events - they should just be
processed normally. As for LLDD reporting events when the pool is
exhausted, they are just lost.
second, if phy was disabled, and no one trigger the reenable by sysfs, the LLDD
has no way to post new sas phy events.
For the extreme scenario of pool becoming exhausted and PHY being
disabled, it should remain disabled until user takes some action to fix
originating problem.
Thanks!
Yijing.
Much appreciated,
John
Thanks!
Yijing.
Thanks,
John
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