Date: Wed, 25 Feb 2015 02:58:53 -0500 From: Alfred Perlstein <alfred@freebsd.org> To: John-Mark Gurney <jmg@funkthat.com>, "K. Macy" <kmacy@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, Harrison Grundy <harrison.grundy@astrodoggroup.com>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: locks and kernel randomness... Message-ID: <54ED80BD.1080603@freebsd.org> In-Reply-To: <20150225002301.GS46794@funkthat.com> References: <20150224015721.GT74514@kib.kiev.ua> <54EBDC1C.3060007@astrodoggroup.com> <20150224024250.GV74514@kib.kiev.ua> <DD06E2EA-68D6-43D7-AA17-FB230750E55A@bsdimp.com> <20150224174053.GG46794@funkthat.com> <54ECBD4B.6000007@freebsd.org> <20150224182507.GI46794@funkthat.com> <54ECEA43.2080008@freebsd.org> <20150224231921.GQ46794@funkthat.com> <CAHM0Q_NhUpr_HJZZcAEoZ_hNvZKcVzUBH-7LALsbkgqjLimA7A@mail.gmail.com> <20150225002301.GS46794@funkthat.com>
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On 2/24/15 7:23 PM, John-Mark Gurney wrote: > K. Macy wrote this message on Tue, Feb 24, 2015 at 15:33 -0800: >>> If someone does find a performance issue w/ my patch, I WILL work with >>> them on a solution, but I will not work w/ people who make unfounded >>> claims about the impact of this work... >>> >> <shrug> ... The concerns may be exaggerated, but they aren't >> unfounded. Not quite the same thing, but no one wants to spend the > Till someone shows me code in the kernel tree where this is even close > to a performance problem, it is unfounded... I've asked, and no one > has > >> cycles doing a SHA256 because it's "The Right Thing"(tm) when their >> use case only requires a fletcher2. > Depends upon what you're doing.. I haven't proposed changing ZFS's > default to sha256, so stop w/ the false equivalences... > >> If it doesn't already exist, it might also be worth looking in to a >> more scalable CSPRNG implementation not requiring locking in the >> common case. For example, each core is seeded separately periodically >> so that has a private pool that is protected by a critical section. >> The private pool would be regularly refreshed by cpu-local callout. >> Thus, a lock would only be acquired if the local entropy were >> depleted. > I'm not discussing this until you read and reply to my original email, > since it's clear that my original email's contents has been ignored in > this thread... > What is final proposal? More spinlocks? That is not a good idea. Doing a single buildworld is not enough. Ask netflix or someone with a real load of 1000s of threads/processing to do testing for you if you truly want to touch scheduler. -Alfred
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