gpg-agent prompt slow to show up

[Charlie Brown]

Hello everyone,
I'm new to gpg, and I'm trying the agent.

I noticed that when gpg needs to prompt me for pass phrase, the prompt
shows up about 15 seconds after I issue the command (e.g. gpg
--decrypt or git commit -S). The problem exists with both gpg
--use-agent and gpg2.

I then tried the --no-use-agent flag of gpg, and the cli prompt showed
up instantly, but sadly it doesn't not use the agent by its nature.

My colleagues say that they do not have such problem. Any idea, or how
can I look into this problem?

This is the output from gpg-agent --daemon -vv:
<-- Issue a command that will prompt for pass phrase -->
gpg-agent[6458]: handler 0x7f42eb30c700 for fd 5 started
gpg-agent[6458]: starting a new PIN Entry
<-- Long annoying delay -->
<-- Then the prompt show up -->
gpg-agent[6458]: handler 0x7f42ebb0d700 for fd 8 started
gpg-agent[6458]: socket is still served by this server
gpg-agent[6458]: handler 0x7f42ebb0d700 for fd 8 terminated

Here's the version of the gpg components:
gpg-agent 2.1.9
libgcrypt 1.6.4
gpg 1.4.19
gpg2 2.1.9

Sincerely,
王文鑫
Wenxin Wang
Department of Electronic Engineering,
Tsinghua University,
Beijing 100084, P. R. China
(+86)18811369901
Email：wangwx12 at mails.tsinghua.edu.cn