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* [PATCH v2 0/2] mwifiex: spinlock usage improvements
@ 2019-06-25 17:40 Brian Norris
  2019-06-25 17:40 ` [PATCH v2 1/2] mwifiex: dispatch/rotate from reorder table atomically Brian Norris
  2019-06-25 17:40 ` [PATCH v2 2/2] mwifiex: don't disable hardirqs; just softirqs Brian Norris
  0 siblings, 2 replies; 4+ messages in thread
From: Brian Norris @ 2019-06-25 17:40 UTC (permalink / raw)
  To: Ganapathi Bhat, Nishant Sarmukadam, Amitkumar Karwar, Xinming Hu
  Cc: linux-kernel, linux-wireless, Brian Norris

This series follows up on some notes from this thread:

  http://lkml.kernel.org/linux-wireless/20181130175957.167031-1-briannorris@chromium.org
  Subject: [4.20 PATCH] Revert "mwifiex: restructure rx_reorder_tbl_lock usage"

where Ganapathi suggested I send out my work.

In particular, patch 1 is a step toward helping apply Ganapathi's
original "mwifiex: restructure rx_reorder_tbl_lock usage" solution
without regression, by logically separating the two operations (and
therefore, the locking patterns) involved in that deadlock. It doesn't
re-apply that change, nor does it 100% unblock such a solution, but at
least it's a step in the right direction, as I understand it.

Patch 2 is a change I noticed should be possible along the way. There
are a number of reasons we probably shouldn't be disabling hardirqs when
it's not necessary, but one funny side effect: bugs noticed in the above
"revert" patch would no longer happen. This is because
mwifiex_recv_packet() bases softirq decisions on in_interrupt() (see
description in include/linux/preempt.h), so it will automatically skip
softirq processing if we have BH disabled, but not if we only have hard
IRQs disabled. In other words, if we have such an incorrect nesting bug
in the future (this time with BH disabled), we will now skip softirq
processing and therefore sidestep this sort of bug. [1]

[Related note: softirq masking is weird:
https://lwn.net/Articles/779738/]

It's also possible we can improve system responsiveness and
debuggability by keeping (hard) IRQs enabled more often, although I
didn't measure any particular effect here, and most of these contexts
should be rather quick.

I've done a variety of performance and stress tests for this series, on
both 8897/SDIO and 8997/PCIe, and I haven't seen any decrease in
performance or stability. Or, any change in performance appears to be
within the range of "noise".

Regards,
Brian

[1] Side note: the usage of 'in_interrupt()' in mwifiex_recv_packet() is
probably not really a good idea. But it does have a helpful side effect
for this particular sort of bug.

Changelog:

v2:
 * fix warnings about using uninitialized "flags" variables


Brian Norris (2):
  mwifiex: dispatch/rotate from reorder table atomically
  mwifiex: don't disable hardirqs; just softirqs

 drivers/net/wireless/marvell/mwifiex/11n.c    |  53 +++-----
 drivers/net/wireless/marvell/mwifiex/11n.h    |   5 +-
 .../net/wireless/marvell/mwifiex/11n_aggr.c   |  26 ++--
 .../net/wireless/marvell/mwifiex/11n_aggr.h   |   2 +-
 .../wireless/marvell/mwifiex/11n_rxreorder.c  | 125 ++++++++----------
 .../net/wireless/marvell/mwifiex/cfg80211.c   |  35 +++--
 drivers/net/wireless/marvell/mwifiex/cmdevt.c |  76 +++++------
 drivers/net/wireless/marvell/mwifiex/init.c   |  32 ++---
 drivers/net/wireless/marvell/mwifiex/main.c   |  29 ++--
 drivers/net/wireless/marvell/mwifiex/scan.c   |  58 ++++----
 .../wireless/marvell/mwifiex/sta_cmdresp.c    |   5 +-
 .../net/wireless/marvell/mwifiex/sta_event.c  |  10 +-
 drivers/net/wireless/marvell/mwifiex/tdls.c   |  68 ++++------
 drivers/net/wireless/marvell/mwifiex/txrx.c   |   5 +-
 .../net/wireless/marvell/mwifiex/uap_txrx.c   |  10 +-
 drivers/net/wireless/marvell/mwifiex/usb.c    |  10 +-
 drivers/net/wireless/marvell/mwifiex/util.c   |  15 +--
 drivers/net/wireless/marvell/mwifiex/wmm.c    | 109 ++++++---------
 18 files changed, 278 insertions(+), 395 deletions(-)

-- 
2.22.0.410.gd8fdbe21b5-goog


^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2019-06-27 16:51 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-06-25 17:40 [PATCH v2 0/2] mwifiex: spinlock usage improvements Brian Norris
2019-06-25 17:40 ` [PATCH v2 1/2] mwifiex: dispatch/rotate from reorder table atomically Brian Norris
2019-06-27 16:51   ` Kalle Valo
2019-06-25 17:40 ` [PATCH v2 2/2] mwifiex: don't disable hardirqs; just softirqs Brian Norris

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