RE: [????] Re: [PATCH][v2] RDMA/core: Prevent soft lockup during large user memory region cleanup

["Li,Rongqing" <lirongqing@baidu.com>]

> > Fix soft lockup issues by incorporating cond_resched() calls within
> > __ib_umem_release(), and this SG entries are typically grouped in 2MB
> > chunks on x86_64, adding cond_resched() should has minimal
> performance
> > impact.
> 
> This is not true, I think this should have been more careful to only resched
> after larger groupings.. How much slower did you make normal 4k unpins??
> 
> Jason


I don't see this as a issue for several reasons. First, this code path is not performance-critical. Second, the number of cond_resched calls added by this modification is identical to what was introduced in commit 928da37a229f3444, which has never been reported to cause any problems. Third, as seen in commit 16c610162d1f1c, the cond_resched call rate was reduced to once every 16 packets - our current frequency remains well below this commit.

When I have access to the appropriate hardware, I will collect performance data for further analysis. Alternatively, if this is considered problematic, someone could collaborate on optimizing these two cond_resched in umem.c calls together.

Thanks

-Li