Re: [PATCH for 5.1 0/3] Restartable Sequences updates for 5.1
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From: Peter Zijlstra <peterz@infradead.org>
Date: 2019-03-06 08:22:06
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On Tue, Mar 05, 2019 at 05:32:10PM -0500, Mathieu Desnoyers wrote:
----- On Mar 5, 2019, at 4:58 PM, Peter Zijlstra peterz@infradead.org wrote:quoted
On Tue, Mar 05, 2019 at 03:18:35PM -0500, Mathieu Desnoyers wrote:quoted
* NUMA node ID in TLS Having the NUMA node ID available in a TLS variable would allow glibc to perform interesting NUMA performance improvements within its locking implementation, so I have a patch adding NUMA node ID support to rseq as a new rseq system call flag.Details? There's just not much room in the futex word, and futexes themselves are not numa aware.It was discussed in this libc-alpha mailing list thread: https://public-inbox.org/libc-alpha/CAMe9rOo7i_-keOooa0D+P_wzatVCdKkTRiFiJ-cxpnvi+eApuQ@mail.gmail.com/ (adding the relevant people in CC) I'd like to hear in more details on how they intend to design NUMA-aware spinlocks within glibc. All I know is that quick access to the node ID would help for this.
Userspace spinlocks are a trainwreck anyway. The only case where they can possibly work is when there's only a single thread on every cpu. Pretty much any other scenario is fail; see why we have paravirt spinlocks.