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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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WARNING: multiple messages have this Message-ID (diff)
From: George Spelvin <lkml@SDF.ORG>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@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.

  reply	other threads:[~2020-03-31  0:27 UTC|newest]

Thread overview: 14+ 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
2019-12-10 12:15 ` George Spelvin
2020-03-30 10:57 ` Mark Rutland
2020-03-30 10:57   ` Mark Rutland
2020-03-30 19:32   ` George Spelvin
2020-03-30 19:32     ` George Spelvin
2020-03-31  0:27     ` George Spelvin [this message]
2020-03-31  0:27       ` George Spelvin
2020-03-31 10:14     ` Mark Rutland
2020-03-31 10:14       ` Mark Rutland
2020-03-31 14:49       ` George Spelvin
2020-03-31 14:49         ` George Spelvin
2020-03-31 16:26         ` Mark Rutland
2020-03-31 16:26           ` Mark Rutland

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