Saturday, August 23, 2014

Memory access latencies

Once, I saw a table in which all cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 memory latencies are scaled in such a way that CPU cycle is defined to be 1 second, and cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365n L1 cache latency is several seconds, L2 cache even more, and so on up to SCSI commands timeout and system reboot. This was very interesting because I have much better developed sense for seconds and higher time units that for nanoseconds, microseconds, etc. Few days ago I remembered that table and I wanted to see it again, but couldn't find it.  This was from some book I couldn't remember cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 name. So, I started to google for it, and finally, after an hour or so of googling, I managed to find this picture. It turns out that this was from cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 book Systems performance written by Brendan Gregg. So, I decided to replicate it here for a future reference:


Table 2.2: Example Time Scale of System Latencies
Event Latency Scaled
1 CPU Cycle 0.3 ns 1 s
Level 1 cache access 0.9 ns 3 s
Level 2 cache access 2.8 ns 9 s
Level 3 cache access 12.9 ns 43 s
Main memory access (DRAM, from CPU) 120 ns 6 min
Solid-state disk I/O (flash memory) 50 - 150 us 2-6 days
Rotational disk I/O 1-10 ms 1-12 months
Internet: San Francisco to New York 40 ms 4 years
Internet: San Francisco to United Kingdom 81 ms 8 years
Internet: San Francisco to Australia 183 ms 19 years
TCP packet retransmit 1-3 s 105-317 years
OS virtualization system reboot 4 s 423 years
SCSI command timeout 30 s 3 millennia
Hardware (HW) virtualization system reboot 40 s 4 millennia
Physical system reboot 5 min 32 millennia

It's actually impressive how fast CPU is with respect to ocá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365r components. It is also very good argument for multitasking, i.e. assigning CPU to some ocá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365r task while waiting for, e.g. disk, or something from cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 network.

One additional impressive thing is written below cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 table in cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 book. Namely, if you multiply CPU cycle with speed of light (c) you can see that cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 light can travel only 0.5m while CPU does one instruction. That's really impressive. :)

That's it for this post. For cá cược thể thao bet365_cách nạp tiền vào bet365_ đăng ký bet365 end, while I was searching for this table, I stumbled on some additional interesting links:



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scientist, consultant, security specialist, networking guy, system administrator, philosopher ;)

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