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August 23, 2013

openSuSE Conference 2013 in Thessaloniki, Greece

Filed under: Great Days — colyli @ 6:18 am


In recent months, I worked on hard disk I/O latency measurement for our cloud service infrastructure. The initial motivation is to identify almost-broken-but-still-work hard disks, and isolate them from online services. In order to avoid modify core kernel data structure and execution paths, I hacked device mapper module to measure the I/O latency. The implementation is quite simple, just add timestamp “unsigned long start_time_usec” into struct dm_io, when all sub-io of dm_io completed, calculate latency and store it into corresponded data structure.

4 +++ linux-latency/drivers/md/dm.c

13 @@ -60,6 +61,7 @@ struct dm_io {
14 struct bio *bio;
15 unsigned long start_time;
16 spinlock_t endio_lock;
17 + unsigned long start_time_usec;
18 };

After running on around 10 servers from several different cloud services, there are some interesting data and situation observed, which may be helpful for us to identify the relationship between I/O latency and hard disk healthy condition.
It happens that openSuSE Conference 2013 is about to take place in Thessaloniki, Greece, a great opportunity for me to share the interesting data to friends and other developers from openSuSE community.


olympic_museum-1 olymplic_museum-2
Thessaloniki is a beautiful costal city, it is an enjoyed experience that openSuSE conference happens here. The venue is a sports museum (a.k.a Olympic Museum), very nice place for a community conference. When I entered the museum one day early, I saw many volunteers (someone I knew from SuSE and someone I didn’t know who were local community members), they were busy to prepare many stuffs from meeting rooms to booth. I joined to help a little for half day, then back to hotel to prepare my talk slide.


prepare-0prepare-3 prepare-2

prepare-5 prepare-4 prepare-1


This year, I did better, the slide was accomplished 8 hours before my talk, last time in Prague it was 4~5 hours before 🙂 Much more people showed up beyond my expectation, during and after the talk, a lot communication happened. Some people also suggested me to update the data in next year openSuSE conference. This project is still in quite early stage, I will continue to update information in next time.


This year, I didn’t meet many friends who live in German or Czech Republic, maybe it is because long distance travel and too hot weather. Fortunately one hacker I met this year helped me a lot, he is Olive Neukum. We talked a lot on seq_lock implementation in Linux kernel, he inspired me an idea on non-lock-confliction implementation for seq_lock when reading clock resource in ktime_get(). The idea is simple: if seq number changed after reading the data, just ignore the data and return, do not try again. Because in latency sampling, there is no need to measure I/O latency for every I/O request, if the sampling may be random (lock conflict could be treat as kind of random), the statistic result is still reliable.  Oliver also gave a talk on “speculative execution”, introduced basic idea of speculative execution and the support in glibc and kernel. This is one of the most interesting talks IMHO 🙂

During the conference, there were many useful communication happened, e.g. I talked with Andrew Wafaa about possible ARM cooperation in China, with Max Huang about open source promotion, with Izabel Valverde for travel support program. This year, there was a session talked about openSuSE TSP (Travel Support Program) status update. IMHO, all updates about TSP makes this program to be more sustainable, e.g. more explicit travel policy, asking sponsored people to help as volunteer for organization. Indeed, before TSP mentioned this update, I did in this way for years 🙂 Thanks to openSuSE Travel Support Program, to help me to meet community friends every year, and have the opportunity to share ideas with other hackers and community members.

volunteer ralf
Like Ralf Flaxa said, openSuSE community has its own dependent power and grows healthily. openSuSE conference 2013 is the first time that it happens in a city where no SuSE office located.  I saw many people from local community helped on vane preparation, organization, management, only a few people are SuSE employees. This is impressive, I really feel the power of community, people just show up, take their own role and lead. Next year openSuSE conference 2014 will be in Dubrovnik of Croatia, I believe the community will continue to organize another great event, of cause I will join and help in my way.


[1] slide of my talk can be found here,

[2] live video of my talk, starts from 1:17:30

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