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    SubjectRe: [dm-devel] [PATCH 0/2] Introduce the request handling for dm-crypt
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    On 3 December 2015 at 23:47, Mikulas Patocka <mpatocka@redhat.com> wrote:
    >
    >
    > On Thu, 3 Dec 2015, Baolin Wang wrote:
    >
    >> On 3 December 2015 at 03:56, Alasdair G Kergon <agk@redhat.com> wrote:
    >> > On Wed, Dec 02, 2015 at 08:46:54PM +0800, Baolin Wang wrote:
    >> >> These are the benchmarks for request based dm-crypt. Please check it.
    >> >
    >> > Now please put request-based dm-crypt completely to one side and focus
    >> > just on the existing bio-based code. Why is it slower and what can be
    >> > adjusted to improve this?
    >> >
    >>
    >> OK. I think I find something need to be point out.
    >> 1. From the IO block size test in the performance report, for the
    >> request based, we can find it can not get the corresponding
    >> performance if we just expand the IO size. Because In dm crypt, it
    >> will map the data buffer of one request with scatterlists, and send
    >> all scatterlists of one request to the encryption engine to encrypt or
    >> decrypt. I found if the scatterlist list number is small and each
    >> scatterlist length is bigger, it will improve the encryption speed,
    >
    > This optimization is only applicable to XTS mode. XTS has its weaknesses
    > and it is not recommended for encryption of more than 1TB of data
    > ( http://grouper.ieee.org/groups/1619/email/msg02357.html )
    >
    > You can optimize bio-based dm-crypt as well (use larger encryption chunk
    > than 512 bytes when the mode is XTS).
    >
    > The most commonly used mode aes-cbc-essiv:sha256 can't be optimized that
    > way. You have to do encryption and decryption sector by sector because
    > every sector has different IV.

    Make sense. We'll optimize bio-based dm-crypt for XTS mode, and do
    some investigations for none XTS mode.

    >
    > Mikulas
    >



    --
    Baolin.wang
    Best Regards


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