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Martin Hope
PeopleMoutainPeopleSea
Asked: 2024-10-01 18:12:29 +0800 CST
  • 6

ss -tm shows detailed memory information about each TCP session. I found that some of the tcp sessions show sock_drop, here is one:

ESTAB    ***** some irrelevant info here ****               
     skmem:(r0,rb3446699,t0,tb87040,f0,w0,o0,bl0,d222)

d222 in skmem, according the the man page, is the sock_drop number.

But ip -s link (or ifconfig) both shows 0 packet drops

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:d9:fb:52 brd ff:ff:ff:ff:ff:ff
    RX:   bytes   packets errors dropped  missed   mcast           
    79371129016 110948258      0       0       0       0 
    TX:   bytes   packets errors dropped carrier collsns           
    78030205763  96204113      0       0       0       0

So here is my question: What is the difference between packet drops showed in ip -s link and sock_drop showed in ss -tm? What are the possible reasons that causes packet drop and sock_drop? Is sock_drop related to tcp retransmission?

linux
Martin Hope
PeopleMoutainPeopleSea
Asked: 2024-09-25 00:53:53 +0800 CST
  • 4

For the aws EC2 and aliyun instances or other similar cloud computing services, is the VM guaranteed to run on the same physical machine each time you launch it, or it may migrate from one physical machine to another?

Also I know hypervisors support live migration, so is it possible that my running aws/aliyun instance migrated by the service provider, which may cause a short time outage or unresponsiveness.

Here is the reason for my question: I have a aliyun server collecting realtime data packets stream from another aws server. Each packet has a sender timestamp tag. At the receiver side, receiver uses the (current_local_timestamp - sender_timestamp) to get the elapsed time. Usually this elapsed time is around 30~50ms, sometimes ~100ms. But in the extreme cases, this elapsed time can go up to a few seconds or even more than 1 minutes, this case happens at least 2~3 times a month, often at Friday (but not always) or some holidays.

I'm trying to figuring out the reason for the extreme large transport delay.

amazon-web-services