On 2019/5/31 17:54, Salil Mehta wrote: >> From: [email protected] On Behalf Of Yunsheng Lin >> Sent: Friday, May 31, 2019 10:01 AM >> To: [email protected] >> Cc: [email protected]; [email protected]; >> [email protected]; [email protected]; linux- >> [email protected]; Linuxarm <[email protected]> >> Subject: [PATCH v2 net-next] net: link_watch: prevent starvation when >> processing linkwatch wq >> >> When user has configured a large number of virtual netdev, such >> as 4K vlans, the carrier on/off operation of the real netdev >> will also cause it's virtual netdev's link state to be processed >> in linkwatch. Currently, the processing is done in a work queue, >> which may cause cpu and rtnl locking starvation problem. >> >> This patch releases the cpu and rtnl lock when link watch worker >> has processed a fixed number of netdev' link watch event. >> >> Currently __linkwatch_run_queue is called with rtnl lock, so >> enfore it with ASSERT_RTNL(); > > > Typo enfore --> enforce ?
My mistake. thanks. > > > >> Signed-off-by: Yunsheng Lin <[email protected]> >> --- >> V2: use cond_resched and rtnl_unlock after processing a fixed >> number of events >> --- >> net/core/link_watch.c | 17 +++++++++++++++++ >> 1 file changed, 17 insertions(+) >> >> diff --git a/net/core/link_watch.c b/net/core/link_watch.c >> index 7f51efb..07eebfb 100644 >> --- a/net/core/link_watch.c >> +++ b/net/core/link_watch.c >> @@ -168,9 +168,18 @@ static void linkwatch_do_dev(struct net_device >> *dev) >> >> static void __linkwatch_run_queue(int urgent_only) >> { >> +#define MAX_DO_DEV_PER_LOOP 100 >> + >> + int do_dev = MAX_DO_DEV_PER_LOOP; >> struct net_device *dev; >> LIST_HEAD(wrk); >> >> + ASSERT_RTNL(); >> + >> + /* Give urgent case more budget */ >> + if (urgent_only) >> + do_dev += MAX_DO_DEV_PER_LOOP; >> + >> /* >> * Limit the number of linkwatch events to one >> * per second so that a runaway driver does not >> @@ -200,6 +209,14 @@ static void __linkwatch_run_queue(int urgent_only) >> } >> spin_unlock_irq(&lweventlist_lock); >> linkwatch_do_dev(dev); >> + > > > A comment like below would be helpful in explaining the reason of the code. > > /* This function is called with rtnl_lock held. If excessive events > * are present as part of the watch list, their processing could > * monopolize the rtnl_lock and which could lead to starvation in > * other modules which want to acquire this lock. Hence, co-operative > * scheme like below might be helpful in mitigating the problem. > * This also tries to be fair CPU wise by conditional rescheduling. > */ Yes, thanks for the helpful comment. > > >> + if (--do_dev < 0) { >> + rtnl_unlock(); >> + cond_resched(); >> + do_dev = MAX_DO_DEV_PER_LOOP; >> + rtnl_lock(); >> + } >> + >> spin_lock_irq(&lweventlist_lock); >> } > > . >
