Re: [PATCH RFC] futex: avoid false sharing between hb->chain and the bucket lock

[Peter Zijlstra]

On Wed, Jun 10, 2026 at 01:22:34PM +0200, Thomas Gleixner wrote:
> On Tue, Jun 09 2026 at 22:18, Peter Zijlstra wrote:
> > On Tue, Jun 09, 2026 at 10:11:17PM +0200, Peter Zijlstra wrote:
> >> Anyway, how does something like the below work for you? It's a total
> >> hack job, but it (sorta) builds and runs.
> >> 
> >
> > Please use this one, I spotted a silly bug.
> 
> So I ran this on two machines.
> 
> SKL dual socket 112 threads:
> 
> 		Baseline	Patched
> 
> shared (16k)	1571857 	1641435         + 4.4%
> autosize (512)	 646390 	 903371         +39.7%
> -b 256		 464395 	 587014         +26.4%
> -b 512		 715687 	 995943         +39.2%
> -b 1024		 995085 	1396328         +40.3%
> -b 2048		1293114         1668395         +29.0%
> -b 4096		2124438 	2240228         + 5.5%
> 
> Zen3 dual socket 256 threads:
> 
> 		Baseline	Patched
> 
> shared	(16k)	1275840		1381279	 	+ 8.2%
> autosize (512)	1252745		1482179		+18.3%
> -b 256		 856274		 955455		+11.5%
> -b 512		1267490		1544010		+21.8%
> -b 1024		1424013		1625424		+14.1%
> -b 2048		1505181		1669342		+10.9%
> -b 4096		1465993		1688932		+15.2%

I suppose that means I'd better go make it prettier and survive
randconfig :-)