Re: [PATCH v3] bcache: dynamic incremental gc

[Zou Mingzhe <mingzhe.zou@easystack.cn>]

在 2022/5/23 10:52, Zou Mingzhe 写道:
> 在 2022/5/21 02:24, Eric Wheeler 写道:
>> On Fri, 20 May 2022, Zou Mingzhe wrote:
>>
>> Questions:
>>
>> 1. Why is the after-"BW NO GC" graph so much flatter than the before-"BW
>>     NO GC" graph?  I would expect your control measurements to be 
>> about the
>>     same before vs after.  You might `blkdiscard` the cachedev and
>>     re-format between runs in case the FTL is getting in the way, or 
>> maybe
>>     something in the patch is affecting the "NO GC" graphs.
>> 2. I wonder how the latency looks if you zoom into to the latency graph:
>>     If you truncate the before-"LATENCY DO GC" graph at 3000 us then how
>>     does the average latency look between the two?
>> 3. This may be solved if you can fix the control graph issue in #1, but
>>     the before vs after of "BW DO GC" shows about a 30% decrease in
>>     bandwidth performance outside of the GC spikes.  "IOPS DO GC" is 
>> lower
>>     with the patch too.  Do you think that your dynamic incremental gc
>>     algorithm be tuned to deal with GC latency and still provide 
>> nearly the
>>     same IOPS and bandwidth as before?
>>
>>
>> -- 
>> Eric Wheeler

Hi Eric,

I have done a retest round and update all data on 
"https://gist.github.com/zoumingzhe/69a353e7c6fffe43142c2f42b94a67b5".

First, there is only this patch between before and after, I re-format 
the disk with make-bcache before each fio. Each case was tested 5 times, 
and the results are as follows:

                     before after
       NO GC           DO GC          NO GC          DO GC
1    99162.29     97366.28     99970.89     98290.81
2    99897.80     97879.99     96829.14     95548.88
3    98183.49     98834.29     101508.06   98581.53
4    98563.17     98476.61     96866.40     96676.87
5    97059.91     98356.50     96248.10     94442.61

Some details are also shown in the new graph, in addition to the raw 
data available for download.

I confirm that this patch does not cause a drop in iops. We have some 
other patches that may have affected the previous test, but this patch 
works fine.

In fact, we mostly modified the gc handling.

mingzhe