[LU-8565] sanity test 255a fails with ‘Speedup with willread is less than X%, got Y%’

• Type: Bug
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.9.0
• Affects Version/s: Lustre 2.9.0
• Environment: autotest
• Severity: 3
• Assignee: Li Xi (Inactive)
• Reporter: James Nunez (Inactive)

Description

sanity test 255a fails with

sanity test_255a: @@@@@@ FAIL: Speedup with willread is less than 88%, got 7% 

where the percentage values differ for each failure.

From one of the test failures, we can see that using the WILLREAD advice does not help with read and, for this test, does not out perform the benefits of reading from cache

Iter 1/10: cache speedup: 98%
Iter 1/10: ladvise speedup: -7%

Iter 3/10: cache speedup: 131%
Iter 3/10: ladvise speedup: 8%

Iter 8/10: cache speedup: 108%
Iter 8/10: ladvise speedup: 0%

For this test, we are comparing the speed up gained with the WILLREAD advice versus (half) the benefit of reading from cache:

local lowest_speedup=$((average_cache / 2))
	[ $average_ladvise -gt $lowest_speedup ] ||
		error "Speedup with willread is less than $lowest_speedup%,"\
			"got $average_ladvise%"

So, the expected speed up of the willread advice to ladvise is not as great as expected.

The WILLREAD hint was added with patch http://review.whamcloud.com/#/c/12458

Logs for recent failures are at
https://testing.hpdd.intel.com/test_sets/3ed61acc-6d90-11e6-b058-5254006e85c2
https://testing.hpdd.intel.com/test_sets/5eaddd70-6bca-11e6-8a8c-5254006e85c2
https://testing.hpdd.intel.com/test_sets/f10db2be-69cf-11e6-9258-5254006e85c2
https://testing.hpdd.intel.com/test_sets/e2c962c6-696f-11e6-9258-5254006e85c2

Info required for matching: sanity 255a

Issue Links

• is duplicated by: LU-8564 sanity test_255a: Error: 'Speedup with willread is less than 10%, got 8%'
• is related to: LU-9069 ZFS sanity: FAIL: test_255a Speedup with willread is less than XX%, got YY%
• is related to: LU-4931 New feature of giving server/storage side advice of accessing file