Date: Tue, 24 Feb 2015 15:33:02 -0800 From: "K. Macy" <kmacy@freebsd.org> To: John-Mark Gurney <jmg@funkthat.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, Harrison Grundy <harrison.grundy@astrodoggroup.com>, Alfred Perlstein <alfred@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: locks and kernel randomness... Message-ID: <CAHM0Q_NhUpr_HJZZcAEoZ_hNvZKcVzUBH-7LALsbkgqjLimA7A@mail.gmail.com> In-Reply-To: <20150224231921.GQ46794@funkthat.com> References: <20150224012026.GY46794@funkthat.com> <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>
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> 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 cycles doing a SHA256 because it's "The Right Thing"(tm) when their use case only requires a fletcher2. 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.
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