linux-kernel - Re: [PATCH v3 1/7] libsas: Use static sas event pool to appease sas event lost

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Date:   Tue, 11 Jul 2017 16:37:25 +0100
From:   John Garry <john.garry@...wei.com>
To:     Yijing Wang <wangyijing@...wei.com>, <jejb@...ux.vnet.ibm.com>,
        <martin.petersen@...cle.com>
CC:     <chenqilin2@...wei.com>, <hare@...e.com>,
        <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <chenxiang66@...ilicon.com>, <huangdaode@...ilicon.com>,
        <wangkefeng.wang@...wei.com>, <zhaohongjiang@...wei.com>,
        <dingtianhong@...wei.com>, <guohanjun@...wei.com>,
        <yanaijie@...wei.com>, <hch@....de>, <dan.j.williams@...el.com>,
        <emilne@...hat.com>, <thenzl@...hat.com>, <wefu@...hat.com>,
        <charles.chenxin@...wei.com>, <chenweilong@...wei.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH v3 1/7] libsas: Use static sas event pool to appease sas
 event lost

On 10/07/2017 08:06, Yijing Wang wrote:
> Now libsas hotplug work is static, every sas event type has its own
> static work, LLDD driver queue the hotplug work into shost->work_q.
> If LLDD driver burst post lots hotplug events to libsas, the hotplug
> events may pending in the workqueue like
>
> shost->work_q
> new work[PORTE_BYTES_DMAED] --> |[PHYE_LOSS_OF_SIGNAL][PORTE_BYTES_DMAED] -> processing
>                                 |<-------wait worker to process-------->|
> In this case, a new PORTE_BYTES_DMAED event coming, libsas try to queue it
> to shost->work_q, but this work is already pending, so it would be lost.
> Finally, libsas delete the related sas port and sas devices, but LLDD driver
> expect libsas add the sas port and devices(last sas event).
>
> This patch and use static sas event work pool to appease this issue, since
> it's static work pool, it won't make memory exhaust.
>

[ ... ]

>
> +#define	PORT_POOL_SIZE	(PORT_NUM_EVENTS * 5)
> +#define	PHY_POOL_SIZE	(PHY_NUM_EVENTS * 5)
> +
>  /* The phy pretty much is controlled by the LLDD.
>   * The class only reads those fields.
>   */
>  struct asd_sas_phy {
>  /* private: */
> -	struct asd_sas_event   port_events[PORT_NUM_EVENTS];
> -	struct asd_sas_event   phy_events[PHY_NUM_EVENTS];
> -
> -	unsigned long port_events_pending;
> -	unsigned long phy_events_pending;
> +	struct asd_sas_event   port_events[PORT_POOL_SIZE];
> +	struct asd_sas_event   phy_events[PHY_POOL_SIZE];
>
>  	int error;

Hi Yijing,

So now we are creating a static pool of events per PHY/port, instead of 
having 1 static work struct per event per PHY/port. So, for sure, this 
avoids the dynamic event issue of system memory exhaustion which we 
discussed in v1+v2 series. And it seems to possibly remove issue of 
losing SAS events.

But how did you determine the pool size for a PHY/port? It would seem to 
be 5 * #phy events or #port events (which is also 5, I figure by 
coincidence). How does this deal with flutter of >25 events?

Thanks,
John