lkml.org 
[lkml]   [2021]   [Feb]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v3 07/21] x86/fpu/xstate: Introduce helpers to manage dynamic xstate buffers
    On Wed, Feb 03, 2021 at 04:10:24AM +0000, Bae, Chang Seok wrote:
    > Okay, how about:
    > “
    > This alignment bit is set if the state is saved on a 64B-aligned address in
    > the compacted format buffer.
    > "

    I'd prefer:

    /*
    * True if the buffer of the corresponding XFEATURE is located on the next 64
    * byte boundary. Otherwise, it follows the preceding component immediately.
    */
    static bool xstate_aligns[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = false };

    > The threshold here could be more than that. But the intention is a heads-up to
    > (re-)consider (a) a new allocation mechanism and (b) to shrink the memory
    > allocation.
    >
    > Also, the AMX state size is limited to (a bit less than) 64KB and it was
    > discussed that vmalloc() will be okay with AMX [2].

    So if nothing is going to grow over 64K, why are we even talking about this?

    > Maybe it is possible to backtrack this allocation failure out of #NM handling.
    > But the tracepoint can provide a clear context, although limited to those
    > using it.

    Yes, add it when it is really needed. Not slapping it proactively and
    hoping for any potential usage.

    > Indeed, this is the most preferred way on one hand. But there was a change to
    > the current allocation approach by Ingo about 6 years ago [3].

    Yah, there's that. :-\

    I guess it needs to stay embedded. Oh well.

    I guess you can diminish the confusion by doing this:

    struct fpu {

    ...

    union fpregs_state *state;

    union fpregs_state __default_state;
    };

    and tasks will have

    state = &__default_state;

    set up by default in fpu__copy() etc.

    AMX tasks will simply change the pointer to the vmalloc'ed xstate
    buffer. This way at least the pointer will be a single one and the task
    alloc code will simply reroute it instead of having two things to pay
    attention to.

    Thx.

    --
    Regards/Gruss,
    Boris.

    SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg

    \
     
     \ /
      Last update: 2021-02-04 14:12    [W:2.582 / U:0.608 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site