linux-kernel - Re: [PATCH 3/3] fuse: Use hash table to link processing request

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Message-ID: <00ffd41c-b28c-466a-c496-546ce57d7990@virtuozzo.com>
Date:   Tue, 25 Sep 2018 12:35:23 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     kuznet@...tuozzo.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] fuse: Use hash table to link processing request

On 25.09.2018 12:08, Miklos Szeredi wrote:
> On Tue, Sep 11, 2018 at 12:12 PM, Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
>> We noticed the performance bottle neck in FUSE running our
>> Virtuozzo storage over rdma. On some types of workload
>> we observe 20% of times pent in request_find() in profiler.
>> This function is iterating over long requests list, and it
>> scales bad.
>>
>> The patch introduces hash table to reduce the number
>> of iterations, we do in this function. Hash generating
>> algorithm is taken from hash_add() function, while
>> 512 lines table is used to store pending requests.
>> This fixes problem and improves the performance.
> 
> Pushed to fuse.git#for-next with a number of small changes.   E.g. I

Thanks!

> reduced the number of cachlines to 256 to make the hashtable size just
> 4k.   Was there a scientific reason for choosing 512 as the optimal
> number of cache lines?

I just tried to choose a size, which is not small for all of potential
users. But, it looks like 256 should be also enough. 
So, there was no hidden mathematics...

Kirill