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    SubjectRe: [RFC] per-CPU cryptd thread implementation based on workqueue
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    Sorry for my late. Last week is Chinese new year holiday.

    On Sat, 2009-01-24 at 15:07 +0800, Andrew Morton wrote:
    > On Thu, 22 Jan 2009 10:32:17 +0800 Huang Ying <ying.huang@intel.com> wrote:
    >
    > > Use dedicate workqueue for crypto
    > >
    > > - A dedicated workqueue named kcrypto_wq is created.
    > >
    > > - chainiv uses kcrypto_wq instead of keventd_wq.
    > >
    > > - For cryptd, struct cryptd_queue is defined to be a per-CPU queue,
    > > which holds one struct cryptd_cpu_queue for each CPU. In struct
    > > cryptd_cpu_queue, a struct crypto_queue holds all requests for the
    > > CPU, a struct work_struct is used to run all requests for the CPU.
    > >
    >
    > Please always prefer to include performance measurements when proposing
    > a performance-enhancing patch. Otherwise we have no basis upon which
    > to evaluate the patch's worth.

    I will setup a testing to measure the performance gain.

    > > +++ b/crypto/crypto_wq.c
    > > @@ -0,0 +1,39 @@
    > > +/*
    > > + * Workqueue for crypto subsystem
    > > + *
    > > + * Copyright (c) 2009 Intel Corp.
    > > + * Author: Huang Ying <ying.huang@intel.com>
    > > + *
    > > + * 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.
    > > + *
    > > + */
    > > +
    > > +#include <linux/workqueue.h>
    > > +#include <crypto/algapi.h>
    > > +#include <crypto/crypto_wq.h>
    > > +
    > > +struct workqueue_struct *kcrypto_wq;
    > > +EXPORT_SYMBOL_GPL(kcrypto_wq);
    > > +
    > > +static int __init crypto_wq_init(void)
    > > +{
    > > + kcrypto_wq = create_workqueue("crypto");
    > > + if (unlikely(!kcrypto_wq))
    > > + return -ENOMEM;
    > > + return 0;
    > > +}
    > > +
    > > +static void __exit crypto_wq_exit(void)
    > > +{
    > > + if (likely(kcrypto_wq))
    > > + destroy_workqueue(kcrypto_wq);
    >
    > I don't believe that it is possible to get here with kcrypto_wq==NULL.

    Yes. I will fix this.

    > >
    > > ...
    > >
    > > +int cryptd_enqueue_request(struct cryptd_queue *queue,
    > > + struct crypto_async_request *request)
    > > +{
    > > + int cpu, err, queued;
    > > + struct cryptd_cpu_queue *cpu_queue;
    > > +
    > > + cpu = get_cpu();
    > > + cpu_queue = per_cpu_ptr(queue->cpu_queue, cpu);
    > > + spin_lock_bh(&cpu_queue->lock);
    > > + err = crypto_enqueue_request(&cpu_queue->queue, request);
    > > + spin_unlock_bh(&cpu_queue->lock);
    > > + /* INUSE should be set after queue->qlen assigned, but
    > > + * spin_unlock_bh imply a memory barrior already */
    > > + if (!test_and_set_bit_lock(CRYPTD_STATE_INUSE, &cpu_queue->state)) {
    > > + queued = queue_work(kcrypto_wq, &cpu_queue->work);
    > > + BUG_ON(!queued);
    > > + }
    >
    > Do we actually need to use CRYPTD_STATE_INUSE here? The
    > WORK_STRUCT_PENDING handling in the workqueue does basically the same
    > thing?

    Yes. It is not necessary, I will fix this.

    > > + put_cpu();
    > > +
    > > + return err;
    > > +}
    > > +
    > > +int cryptd_tfm_in_queue(struct cryptd_queue *queue, struct crypto_tfm *tfm)
    >
    > Did this need to have global scope?

    It should be static. I will fix this.

    > > +{
    > > + int cpu, in_queue;
    > > + struct cryptd_cpu_queue *cpu_queue;
    > > +
    > > + for_each_possible_cpu(cpu) {
    > > + cpu_queue = per_cpu_ptr(queue->cpu_queue, cpu);
    > > + spin_lock_bh(&cpu_queue->lock);
    > > + in_queue = crypto_tfm_in_queue(&cpu_queue->queue, tfm);
    > > + spin_unlock_bh(&cpu_queue->lock);
    > > + if (in_queue)
    > > + return 1;
    > > + }
    > > + return 0;
    > > +}
    >
    > Did you consider using for_each_online_cpu() and implementing CPU
    > hotplug? There might be situations where the number of possible CPUs
    > is much greater than the number of online CPUs.

    For cryptd_queue_init() and cryptd_queue_fini(), I think
    for_each_possible_cpu() is sufficient and simpler. Because they are only
    need to be executed once and in slow path. For cryptd_in_queue,
    for_each_online_cpu() can be used.

    > > +static void cryptd_queue_work_done(struct cryptd_cpu_queue *cpu_queue)
    > > +{
    > > + int queued;
    > > +
    > > + if (!cpu_queue->queue.qlen) {
    > > + clear_bit_unlock(CRYPTD_STATE_INUSE, &cpu_queue->state);
    > > + /* queue.qlen must be checked after INUSE bit cleared */
    > > + smp_mb();
    > > + if (!cpu_queue->queue.qlen ||
    > > + test_and_set_bit_lock(CRYPTD_STATE_INUSE,
    > > + &cpu_queue->state))
    > > + return;
    > > + }
    > > +
    > > + queued = queue_work(kcrypto_wq, &cpu_queue->work);
    > > + BUG_ON(!queued);
    > > +}
    >
    > It is unclear (to me) why this code is using the special "locked"
    > bitops. This should be explained in a code comment.
    >
    > It isn't immediately clear (to me) what this function does, what its
    > role is in the overall scheme. It wouldn't hurt at all to put a nice
    > comment over non-trivial functions explaining such things.

    This function is used for CRYPTD_STATE_INUSE logic, because
    CRYPTD_STATE_INUSE is not needed, this function is not needed too. Just
    calling queue_work() at end of cryptd_queue_work() is sufficient.

    > > +static void cryptd_queue_work(struct work_struct *work)
    > > +{
    > > + struct cryptd_cpu_queue *cpu_queue =
    > > + container_of(work, struct cryptd_cpu_queue, work);
    >
    > You could just do
    >
    > struct cryptd_cpu_queue *cpu_queue;
    >
    > cpu_queue = container_of(work, struct cryptd_cpu_queue, work);
    >
    > rather than uglifying the code to fit in 80-cols.

    OK. I will fix this.

    Best Regards,
    Huang Ying

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