From: George Spelvin <lkml@SDF.ORG>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, lkml@sdf.org
Subject: Re: [RFC PATCH v1 44/50] arm64: ptr auth: Use get_random_u64 instead of _bytes
Date: Tue, 31 Mar 2020 00:27:38 +0000 [thread overview]
Message-ID: <20200331002738.GE9199@SDF.ORG> (raw)
In-Reply-To: <20200330193237.GC9199@SDF.ORG>
On Mon, Mar 30, 2020 at 07:32:37PM +0000, George Spelvin wrote:
> On Mon, Mar 30, 2020 at 11:57:45AM +0100, Mark Rutland wrote:
>> As I am unaware, how does the cost of get_random_bytes() compare to the
>> cost of get_random_u64()?
>
> It's approximately 8 times the cost.
Just a expand on on a point I may have left unclear: One
get_random_bytes(), for a length up to 32 bytes, is approximately
8x the one get_random_u64(). (Then it jumps to 16x for up
to 96 bytes.)
Since were're using *two* get_random_u64() calls to replace one
get_random_bytes(), it's a 4x cost difference between the two
alternative ways of generating a 128-bit key.
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next prev parent reply other threads:[~2020-03-31 0:27 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-10 12:15 [RFC PATCH v1 44/50] arm64: ptr auth: Use get_random_u64 instead of _bytes George Spelvin
2020-03-30 10:57 ` Mark Rutland
2020-03-30 19:32 ` George Spelvin
2020-03-31 0:27 ` George Spelvin [this message]
2020-03-31 10:14 ` Mark Rutland
2020-03-31 14:49 ` George Spelvin
2020-03-31 16:26 ` Mark Rutland
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