Re: [Virtio-fs] [PATCH] virtiofsd: Use --thread-pool-size=0 to mean no thread pool

[Vivek Goyal <vgoyal@redhat.com>]

On Thu, Nov 05, 2020 at 02:44:16PM -0500, Vivek Goyal wrote:
> Right now we create a thread pool and main thread hands over the request
> to thread in thread pool to process. Number of threads in thread pool
> can be managed by option --thread-pool-size.
> 
> There is a chance that in case of some workloads, we might get better
> performance if we don't handover the request to a different thread
> and process in the context of thread receiving the request.
> 
> To implement that, redefine the meaning of --thread-pool-size=0 to
> mean that don't use a thread pool. Instead process the request in
> the context of thread receiving request from the queue.
> 
> I can't think how --thread-pool-size=0 is useful and hence using
> that. If it is already useful somehow, I could look at defining
> a new option say "--no-thread-pool".
> 
> I think this patch will be used more as a debug help to do comparison
> when it is more effecient to do not hand over the requests to a
> thread pool.

I ran virtiofs-tests to comapre --thread-pool-size=0 and
--thread-pool-size=64. And results seem to be all over the place. In
some cases thread pool seems to perform batter and in other cases
no-thread-pool seems to perform better.

But in general it looks like that except for the case of libaio workload,
no-thread-pool is helping.

Thanks
Vivek

NAME                    WORKLOAD                Bandwidth       IOPS            
thread-pool             seqread-psync           682.4mb         170.6k          
no-thread-pool          seqread-psync           679.3mb         169.8k          

thread-pool             seqread-psync-multi     2415.9mb        603.9k          
no-thread-pool          seqread-psync-multi     2528.5mb        632.1k          

thread-pool             seqread-mmap            591.7mb         147.9k          
no-thread-pool          seqread-mmap            595.6mb         148.9k          

thread-pool             seqread-mmap-multi      2195.3mb        548.8k          
no-thread-pool          seqread-mmap-multi      2286.1mb        571.5k          

thread-pool             seqread-libaio          329.1mb         82.2k           
no-thread-pool          seqread-libaio          271.5mb         67.8k           

thread-pool             seqread-libaio-multi    1387.1mb        346.7k          
no-thread-pool          seqread-libaio-multi    1508.2mb        377.0k          

thread-pool             randread-psync          59.0mb          14.7k           
no-thread-pool          randread-psync          78.5mb          19.6k           

thread-pool             randread-psync-multi    226.4mb         56.6k           
no-thread-pool          randread-psync-multi    289.2mb         72.3k           

thread-pool             randread-mmap           48.4mb          12.1k           
no-thread-pool          randread-mmap           57.4mb          14.3k           

thread-pool             randread-mmap-multi     183.5mb         45.8k           
no-thread-pool          randread-mmap-multi     240.5mb         60.1k           

thread-pool             randread-libaio         329.4mb         82.3k           
no-thread-pool          randread-libaio         261.8mb         65.4k           

thread-pool             randread-libaio-multi   252.1mb         63.0k           
no-thread-pool          randread-libaio-multi   278.3mb         69.5k           

thread-pool             seqwrite-psync          54.9mb          13.7k           
no-thread-pool          seqwrite-psync          77.8mb          19.4k           

thread-pool             seqwrite-psync-multi    219.9mb         54.9k           
no-thread-pool          seqwrite-psync-multi    314.8mb         78.7k           

thread-pool             seqwrite-mmap           191.7mb         47.9k           
no-thread-pool          seqwrite-mmap           201.4mb         50.3k           

thread-pool             seqwrite-mmap-multi     346.6mb         86.6k           
no-thread-pool          seqwrite-mmap-multi     387.6mb         96.9k           

thread-pool             seqwrite-libaio         306.4mb         76.6k           
no-thread-pool          seqwrite-libaio         248.2mb         62.0k           

thread-pool             seqwrite-libaio-multi   328.5mb         82.1k           
no-thread-pool          seqwrite-libaio-multi   305.6mb         76.4k           

thread-pool             randwrite-psync         55.6mb          13.9k           
no-thread-pool          randwrite-psync         81.2mb          20.3k           

thread-pool             randwrite-psync-multi   227.0mb         56.7k           
no-thread-pool          randwrite-psync-multi   311.6mb         77.8k           

thread-pool             randwrite-mmap          35.3mb          9038            
no-thread-pool          randwrite-mmap          58.1mb          14.5k           

thread-pool             randwrite-mmap-multi    140.8mb         35.2k           
no-thread-pool          randwrite-mmap-multi    210.5mb         52.6k           

thread-pool             randwrite-libaio        307.1mb         76.7k           
no-thread-pool          randwrite-libaio        279.4mb         69.8k           

thread-pool             randwrite-libaio-multi  361.3mb         90.3k           
no-thread-pool          randwrite-libaio-multi  302.6mb         75.6k           

thread-pool             randrw-psync            34.1mb/11.4mb   8754/2929       
no-thread-pool          randrw-psync            38.7mb/12.9mb   9919/3321       

thread-pool             randrw-psync-multi      126.2mb/42.3mb  31.5k/10.5k     
no-thread-pool          randrw-psync-multi      172.2mb/57.7mb  43.0k/14.4k     

thread-pool             randrw-mmap             24.1mb/8270kb   6194/2067       
no-thread-pool          randrw-mmap             42.0mb/14.0mb   10.5k/3606      

thread-pool             randrw-mmap-multi       127.9mb/42.8mb  31.9k/10.7k     
no-thread-pool          randrw-mmap-multi       179.4mb/60.0mb  44.8k/15.0k     

thread-pool             randrw-libaio           64.0mb/21.4mb   16.0k/5485      
no-thread-pool          randrw-libaio           79.6mb/26.6mb   19.9k/6831      

thread-pool             randrw-libaio-multi     174.2mb/58.3mb  43.5k/14.5k     
no-thread-pool          randrw-libaio-multi     201.6mb/67.5mb  50.4k/16.8k