Messages in this thread | | | Subject | Re: [PATCH] x86/mce: Distirbute the clear operation of mces_seen to Per-CPU rather than only monarch CPU | From | Chen Yucong <> | Date | Mon, 19 May 2014 15:54:54 +0800 |
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On Mon, 2014-05-19 at 09:26 +0200, Borislav Petkov wrote: > On Mon, May 19, 2014 at 09:55:40AM +0800, Chen Yucong wrote: > > But all other CPUs also have to wait monarch CPU to exit from mce_end. > > What's the difference between monarch CPU and Per-CPU for clearing > > mces_seen? In practice, there is no difference between them. If we use > > monarch CPU to clear mces_seen, then Per-CPU variable can not play out > > its advantage. > > I'll let you stare at mce_reign() a little bit longer... Also, pay > attention to its callsite, that might help. > We can find the following code segment in mce_end: ----- ... if (order == 1) { /* CHECKME: Can this race with a parallel hotplug? */ int cpus = num_online_cpus();
/* * Monarch: Wait for everyone to go through their scanning * loops. */ while (atomic_read(&mce_executing) <= cpus) { if (mce_timed_out(&timeout)) goto reset; ndelay(SPINUNIT); }
mce_reign(); barrier(); ret = 0; ... ----- If a timeout occurs in monarch CPU, what will happen for the above code segment? The monarch CPU will directly execute -goto reset-, so mce_reign will not be invoked. That way, the clear operation of mces_seen will be skipped, and the stale value of mces_seen will reappear on the next mce.
thx! cyc
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