From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 07/18] io_uring: support for IO polling
Date: Tue, 29 Jan 2019 11:31:51 -0700
Message-ID: <f21fc281-bbaa-3af5-3d64-a55933f1cbfb@kernel.dk>
References: <20190128213538.13486-1-axboe@kernel.dk>
 <20190128213538.13486-8-axboe@kernel.dk> <20190129172414.GA15347@lst.de>
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To: Christoph Hellwig <hch@lst.de>
Cc: linux-aio@kvack.org, linux-block@vger.kernel.org, linux-man@vger.kernel.org, linux-api@vger.kernel.org, jmoyer@redhat.com, avi@scylladb.com
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On 1/29/19 10:24 AM, Christoph Hellwig wrote:
>>  
>> @@ -118,12 +120,16 @@ struct io_kiocb {
>>  	struct list_head	list;
>>  	unsigned int		flags;
>>  #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
>> +#define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
>> +#define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
>>  	u64			user_data;
>> +	u64			res;
> 
> Should this be ret or error instead?  res is kinda off.  A little
> comment describing it won't hurt either.  Last but not least with
> the actual errno value stored here we probably don't need the
> REQ_F_IOPOLL_EAGAIN flag, do we?

Yes good point, that flag pre-dates us having the error in there. I'll
rename the field, too.

>> +	/*
>> +	 * Only spin for completions if we don't have multiple devices hanging
>> +	 * off our complete list, and we're under the requested amount.
>> +	 */
>> +	spin = !ctx->poll_multi_file && (*nr_events < min);
> 
> no need for the braces here.

Killed

>> +static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
>> +				long min)
>> +{
>> +	int ret;
>> +
>> +	do {
>> +		if (list_empty(&ctx->poll_list))
>> +			return 0;
>> +
>> +		ret = io_do_iopoll(ctx, nr_events, min);
>> +		if (ret < 0)
>> +			break;
>> +	} while (min && *nr_events < min);
>> +
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	return *nr_events < min;
> 
> The code looks a little clumsy to me.  Why not:
> 
> 	while (!list_empty(&ctx->poll_list)) {
> 		int ret = io_do_iopoll(ctx, nr_events, min);
> 		if (ret)
> 			return ret;
> 
> 		if (!min || *nr_events >= min)
> 			return 0;
> 	}
> 
> 	return 1;

I think you messed up the 0/1 here, how about this:

	while (!list_empty(&ctx->poll_list)) {
		int ret;

		ret = io_do_iopoll(ctx, nr_events, min);
		if (ret < 0)
			return ret;
		if (!min || *nr_events >= min)
			return 1;
	}

	return 0;

-- 
Jens Axboe

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