linux-kernel - Re: [PATCH v2 2/4] crypto: hisilicon: Add queue management driver for HiSilicon QM module

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Date:   Fri, 1 Feb 2019 15:15:54 +0800
From:   Zhou Wang <wangzhou1@...ilicon.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
CC:     "David S . Miller" <davem@...emloft.net>,
        <linux-crypto@...r.kernel.org>, <linuxarm@...wei.com>,
        <linux-kernel@...r.kernel.org>,
        Kenneth Lee <liguozhu@...ilicon.com>,
        Shiju Jose <shiju.jose@...wei.com>,
        Hao Fang <fanghao11@...wei.com>
Subject: Re: [PATCH v2 2/4] crypto: hisilicon: Add queue management driver for
 HiSilicon QM module

On 2019/2/1 13:22, Herbert Xu wrote:
> On Wed, Jan 23, 2019 at 09:08:51PM +0800, Zhou Wang wrote:
>>
>> +/**
>> + * hisi_qp_poll() - Poll current cqe to see if a task is finished.
>> + * @qp: The qp which will poll.
>> + *
>> + * This function polls current cqe for a give qp to see if a task is finished.
>> + * Return -ETIME if timeout.
>> + */
>> +int hisi_qp_poll(struct hisi_qp *qp)
>> +{
>> +	struct qm_cqe *cqe = qp->cqe + qp->qp_status.cq_head;
>> +	struct qm_cqc *cqc = qp->cqc;
>> +	int retries = 1000;
>> +
>> +	while (!(QM_CQE_PHASE(cqe) == (cqc->dw6 & 0x1))) {
>> +		dma_rmb();
>> +		if (!--retries) {
>> +			dev_err(&qp->qm->pdev->dev, "Poll cqe failed!\n");
>> +			return -ETIME;
>> +		}
>> +		udelay(10);
>> +	}
>> +
>> +	qm_cq_head_update(qp);
>> +	atomic_dec(&qp->qp_status.used);
>> +
>> +	qm_db(qp->qm, qp->qp_id, QM_DOORBELL_CMD_CQ, qp->qp_status.cq_head, 0);
>> +	/* set c_flag */
>> +	qm_db(qp->qm, qp->qp_id, QM_DOORBELL_CMD_CQ, qp->qp_status.cq_head, 1);
>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(hisi_qp_poll);
> 
> Polling in softirq context is unacceptable.  Can't your hardware
> send interrupts to signal completion? What is the average speed
> of processing a single 1500-byte packet on your hardware?

Our hardware supports interrupt. In fact, implementation of compress/decompress
interface of crypto_alg in v1 was done using interrupt:

 compress/decompress:
     send task to hardware
     wait task finished(wait_for_completion_timeout)

 In irq handler:
     complete

However, there is get_cpu/put_cpu in scomp, wait and complete in above has to be
changed to poll:

 compress/decompress:
     send task to hardware
     check if task is finished

The average speed of this zip engine is 7.5GB/s, so it will take about 0.2us to
process 1500B.

Best,
Zhou

> 
> Cheers,
>