Fix speed compute (#1408)

[ti-chi-bot]

This is an automated cherry-pick of #1408

What problem does this PR solve?

fix issue: the average speed isn't accurate(#1405)

What is changed and how it works?

change the Calculation method for speed

Check List

Tests

• Manual test (add detailed scripts or steps below)

command
./br backup full --pd "172.16.6.117:2379" --compression-level 3 --storage "local:///home/zak/new_br"
./br restore full --pd "172.16.6.117:2379" --storage "local:///home/zak/new_br"
log
[2021/08/04 10:03:34.913 +08:00] [INFO] [collector.go:67] ["Full backup success summary"] [total-ranges=45] [ranges-succeed=45] [ranges-failed=0] [backup-checksum=3.515718214s] [backup-fast-checksum=7.003603ms] [backup-total-ranges=58] [backup-total-regions=77] [total-take=14.017946255s] [total-kv=15463846] [total-kv-size=1.859GB] [average-speed=132.6MB/s] ["backup data size(after compressed)"=496.8MB] [BackupTS=426781599562989570]

[2021/08/04 10:06:45.055 +08:00] [INFO] [collector.go:67] ["Full restore success summary"] [total-ranges=37] [ranges-succeed=37] [ranges-failed=0] [split-region=362.373805ms] [restore-checksum=6.890396086s] [restore-ranges=29] [total-take=17.328491842s] ["restore data size(after compressed)"=496.7MB] [total-kv=15462460] [total-kv-size=1.858GB] [average-speed=107.2MB/s]

Release note

• fix the bug that the average speed isn't accurate in backup and restore

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• YuJuncen
• kennytm

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[zhouqiang-cl]

/merge

[ti-chi-bot]

@zhouqiang-cl: /merge is only allowed for the committers, you can assign this pull request to the committer in list by filling /assign @committer in the comment to help merge this pull request.

In response to this:

/merge

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[kennytm]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 35796ea