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    SubjectRe: [PATCH 2 of 4] Introduce i386 fibril scheduling
    On Fri, 2 Feb 2007, Davide Libenzi wrote:

    > On Fri, 2 Feb 2007, Ingo Molnar wrote:
    >
    > > in fact an app could also /trigger/ the execution of a syscall in a
    > > different context - to create parallelism artificially - without any
    > > blocking event. So we could do:
    > >
    > > cookie1 = sys_async(sys_read, params);
    > > cookie2 = sys_async(sys_write, params);
    > >
    > > [ ... calculation loop ... ]
    > >
    > > wait_on_async_syscall(cookie1);
    > > wait_on_async_syscall(cookie2);
    > >
    > > or something like that. Without user-space having to create threads
    > > itself, etc. So basically, we'd make kernel threads more useful, and
    > > we'd make threading safer - by only letting syscalls thread.
    >
    > Since I still think that the many-thousands potential async operations
    > coming from network sockets are better handled with a classical event
    > machanism [1], and since smooth integration of new async syscall into the
    > standard POSIX infrastructure is IMO a huge win, I think we need to have a
    > "bridge" to allow async completions being detectable through a pollable
    > (by the mean of select/poll/epoll whatever) device.
    > In that way you can handle async operations with the best mechanism that
    > is fit for them, and gather them in a single async scheduler.

    To clarify further, below are the API and the use case of my userspace
    implementation. The guasi_fd() gives you back a pollable (POLLIN) fd to be
    integrated in your prefered event retrieval interface. Once it fd is
    signaled, you can fetch your completed requests using guasi_fetch() and
    schedule work based on that.
    The GUASI implementation uses pthreads, but it is clear that an in-kernel
    async syscall implementation can take wiser decisions, and optimize the
    heck out of it (locks, queues, ...).




    - Davide



    /*
    * Example of async pread using GUASI
    */
    static long guasi_wrap__pread(void *priv, long const *params) {

    return (long) pread((int) params[0], (void *) params[1],
    (size_t) params[2], (off_t) params[3]);
    }

    guasi_req_t guasi__pread(guasi_t hctx, void *priv, void *asid, int prio,
    int fd, void *buf, size_t size, off_t off) {

    return guasi_submit(hctx, priv, asid, prio, guasi_wrap__pread, 4,
    (long) fd, (long) buf, (long) size, (long) off);
    }


    ---
    /*
    * guasi by Davide Libenzi (generic userspace async syscall implementation)
    * Copyright (C) 2003 Davide Libenzi
    *
    * This program is free software; you can redistribute it and/or modify
    * it under the terms of the GNU General Public License as published by
    * the Free Software Foundation; either version 2 of the License, or
    * (at your option) any later version.
    *
    * This program is distributed in the hope that it will be useful,
    * but WITHOUT ANY WARRANTY; without even the implied warranty of
    * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    * GNU General Public License for more details.
    *
    * You should have received a copy of the GNU General Public License
    * along with this program; if not, write to the Free Software
    * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
    *
    * Davide Libenzi <davidel@xmailserver.org>
    *
    */

    #if !defined(_GUASI_H)
    #define _GUASI_H


    #define GUASI_MAX_PARAMS 16

    #define GUASI_STATUS_PENDING 1
    #define GUASI_STATUS_ACTIVE 2
    #define GUASI_STATUS_COMPLETE 3


    typedef long (*guasi_syscall_t)(void *, long const *);

    typedef struct s_guasi { } *guasi_t;
    typedef struct s_guasi_req { } *guasi_req_t;

    struct guasi_reqinfo {
    void *priv; /* Call private data. Passed to guasi_submit */
    void *asid; /* Async request ID. Passed to guasi_submit */
    long result; /* Return code of "proc" passed to guasi_submit */
    long error; /* errno */
    int status; /* GUASI_STATUS_* */
    };



    guasi_t guasi_create(int min_threads, int max_threads, int max_priority);
    void guasi_free(guasi_t hctx);
    int guasi_fd(guasi_t hctx);
    guasi_req_t guasi_submit(guasi_t hctx, void *priv, void *asid, int prio,
    guasi_syscall_t proc, int nparams, ...);
    int guasi_fetch(guasi_t hctx, guasi_req_t *reqs, int nreqs);
    int guasi_req_info(guasi_req_t hreq, struct guasi_reqinfo *rinf);
    void guasi_req_free(guasi_req_t hreq);

    #endif


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