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SubjectRe: [RFC] per-CPU cryptd thread implementation based on workqueue
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.

> +++ 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.

>
> ...
>
> +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?

> + put_cpu();
> +
> + return err;
> +}
> +
> +int cryptd_tfm_in_queue(struct cryptd_queue *queue, struct crypto_tfm *tfm)

Did this need to have global scope?

> +{
> + 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.

> +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.

> +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.

> + struct crypto_async_request *req, *backlog;
> +
> + /* Only handle one request at a time to avoid hogging crypto
> + * workqueue */
> + spin_lock_bh(&cpu_queue->lock);
> + backlog = crypto_get_backlog(&cpu_queue->queue);
> + req = crypto_dequeue_request(&cpu_queue->queue);
> + spin_unlock_bh(&cpu_queue->lock);
> +
> + if (!req)
> + goto out;
> +
> + if (backlog)
> + backlog->complete(backlog, -EINPROGRESS);
> + req->complete(req, 0);
> +out:
> + cryptd_queue_work_done(cpu_queue);
> +}
> +
> +static inline struct cryptd_queue *cryptd_get_queue(struct crypto_tfm *tfm)
> {
> struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);
> struct cryptd_instance_ctx *ictx = crypto_instance_ctx(inst);
> - return ictx->state;
> + return ictx->queue;
> }
>
> static int cryptd_blkcipher_setkey(struct crypto_ablkcipher *parent,
> @@ -131,19 +248,13 @@ static int cryptd_blkcipher_enqueue(stru
> {
> struct cryptd_blkcipher_request_ctx *rctx = ablkcipher_request_ctx(req);
> struct crypto_ablkcipher *tfm = crypto_ablkcipher_reqtfm(req);
> - struct cryptd_state *state =
> - cryptd_get_state(crypto_ablkcipher_tfm(tfm));
> - int err;
> + struct cryptd_queue *queue =
> + cryptd_get_queue(crypto_ablkcipher_tfm(tfm));

ditto

>
> ...
>



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