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Subject: Re: [PATCH v3 5/5] md/raid10: convert resync_lock to use seqlock
To:     Guoqing Jiang <guoqing.jiang@linux.dev>,
        Yu Kuai <yukuai1@huaweicloud.com>, song@kernel.org,
        logang@deltatee.com, pmenzel@molgen.mpg.de
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com,
        "yukuai3@huawei.com >> yukuai (C)" <yukuai3@huawei.com>
References: <20220916113428.774061-1-yukuai1@huaweicloud.com>
 <20220916113428.774061-6-yukuai1@huaweicloud.com>
 <e73dc8e8-09a3-ecc8-3199-ac87e8b9ee55@linux.dev>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <a6364e1e-f661-9e32-9d49-5ec421d77025@huaweicloud.com>
Date:   Mon, 19 Sep 2022 09:08:26 +0800
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Hi,

在 2022/09/18 19:36, Guoqing Jiang 写道:
> 
> 
> On 9/16/22 7:34 PM, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Currently, wait_barrier() will hold 'resync_lock' to read 
>> 'conf->barrier',
>> and io can't be dispatched until 'barrier' is dropped.
>>
>> Since holding the 'barrier' is not common, convert 'resync_lock' to use
>> seqlock so that holding lock can be avoided in fast path.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   drivers/md/raid10.c | 87 ++++++++++++++++++++++++++++++---------------
>>   drivers/md/raid10.h |  2 +-
>>   2 files changed, 59 insertions(+), 30 deletions(-)
>>
>> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
>> index 9a28abd19709..2daa7d57034c 100644
>> --- a/drivers/md/raid10.c
>> +++ b/drivers/md/raid10.c
>> @@ -79,6 +79,21 @@ static void end_reshape(struct r10conf *conf);
>>   #include "raid1-10.c"
>> +#define NULL_CMD
>> +#define cmd_before(conf, cmd) \
>> +    do { \
>> +        write_sequnlock_irq(&(conf)->resync_lock); \
>> +        cmd; \
>> +    } while (0)
>> +#define cmd_after(conf) write_seqlock_irq(&(conf)->resync_lock)
> 
> The two is not paired well given only cmd_before needs the 'cmd'.

May be should I just remove cmd_after?
> 
>> +
>> +#define wait_event_barrier_cmd(conf, cond, cmd) \
>> +    wait_event_cmd((conf)->wait_barrier, cond, cmd_before(conf, cmd), \
>> +               cmd_after(conf))
>> +
>> +#define wait_event_barrier(conf, cond) \
>> +    wait_event_barrier_cmd(conf, cond, NULL_CMD)
> 
> What is the issue without define NULL_CMD?
> 

Checkpatch will complain this:

ERROR: space prohibited before that close parenthesis ')'
#38: FILE: drivers/md/raid10.c:94:
+       wait_event_barrier_cmd(conf, cond, )

total: 1 errors, 0 warnings, 169 lines checked

Thanks,
Kuai
> Thanks,
> Guoqing
> .
>