Re: [Crash-utility] [PATCH] task.c: avoid unnecessary cpu cycles during init

在 2020年11月17日 01:00, crash-utility-request(a)redhat.com 写道: >> While stkptr_to_task does the job of trying to match a stack pointer >> to a task, it runs through each task's stack to find whether the given >> SP falls into its range. This can be a very expensive operation, if >> the vmcore is from a system running too many tasks. It can get even >> worse when the total number of CPUs on the system is in the order of >> thousands. Given the expensive nature of the operation, it must be >> optimized as much as possible. Possible options to optimize: >> >> 1) Get min & max of the stack range in first pass and use these >> values against the given SP to decide whether or not to proceed >> with stack lookup. >> 2) Use multithreading to parallely update irq_tasks. >> 3) Skip stkptr_to_task() when SP is 0 >> >> Though option 3 is a low hanging fruit, it significantly improved the >> time taken between starting crash utility & reaching crash prompt. >> Implement option 3 to optimize while listing the other two options >> as TODO items for follow-up. > It looks like on x86_64 the stkptr_to_task() is not called when starting > session and I cannot test, but the patch looks safe enough. > > Acked-by: Kazuhito Hagio <k-hagio-ab(a)nec.com&gt; > > Lianbo, Bhupesh, this is not a fix but huge improvement for some > machines or situations, so I'd like to pick it up for crash-7.2.9. Agree with you, this improvement looks good.

> Could you ack this? and my patch for the compiler warnings? > Yes. After applying your patch, it doesn't reproduce any more. Good findings, Kazu. Thanks. Lianbo > Thanks, > Kazu >