linux-kernel - RE: [PATCH 1/2] perf: Add closing sibling events' file descriptors

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Date:   Tue, 11 Aug 2020 21:06:23 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andi Kleen' <ak@...ux.intel.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        "alexey.budankov@...ux.intel.com" <alexey.budankov@...ux.intel.com>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>
Subject: RE: [PATCH 1/2] perf: Add closing sibling events' file descriptors

> On Tue, Aug 11, 2020 at 02:47:03PM +0000, David Laight wrote:
> > From: Andi Kleen
> > > On Mon, Aug 10, 2020 at 10:36:32PM +0200, Peter Zijlstra wrote:
> > > > On Mon, Aug 10, 2020 at 07:45:18AM -0700, Andi Kleen wrote:
> > > >
> > > > > Unfortunately we're kind of stuck with the old NFILE=1024 default
> > > > > even though it makes little sense on modern servers.
> > > >
> > > > Why can't that be changed? It seems to me all of userspace changes all
> > > > the time; heck that system-doofus thing flushed 20+ years of sysadmin
> > > > experience down the drain, just cause. Why can't we up a file limit?
> > >
> > > We could try, but I believe it's hard coded in various places outside
> > > the kernel.
> >
> > The place it really bites is select().
> > Although the kernel supports large bitmaps glibc doesn't.
> > The random bit overwrites are a PITA to debug.
> 
> Good point.
> 
> I remember I asked for a simple define to increase like glibc5 had, but
> they still didn't implement that.

Even windows lets you redefine FDSET_SIZE before including the header.
And their select() is much more like poll() - so the limit is the number
of sockets, not the highest socket number (which do happen to be small
integers).

	David

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