Meltdown's Impact on Storage Performance - Really an Issue?

Subject: Storage | January 5, 2018 - 08:45 PM |
Tagged: RS4, RS3, patch, meltdown, KB4056892, cpu, 960 EVO, 900P, 850 EVO

While the Meltdown announcements and patches were in full swing, I was busily testing a round of storage devices to evaluate the potential negative impact of the Meltdown patch. Much of the testing we've seen has come in the form of Linux benchmarks, and today we saw a few come out on the Windows side of things. Most of the published data to date shows a ~20% performance hit to small random accesses, but I've noted that the majority of reviewers seem to be focusing on the Samsung 950/960 series SSDs. Sure these are popular devices, but when evaluating changes to a storage subsystem, it's unwise to just stick with a single type of product.

Test conditions were as follows:

  • ASUS Prime Z270-A + 7700K
    • C-States disabled,  no overclock.
    • ASUS MCE disabled, all other clock settings = AUTO.
  • SSDs:
    • Intel Optane 900P 480GB (Intel NVMe driver)
    • Samsung 960 EVO 500GB (Samsung NVMe driver)
    • Samsung 850 EVO 500GB (Intel RST driver)
  • Conditioning:
    • NTFS partition.
    • 16GB test file. Sequential conditioning.
    • Remainder of SSD sequentially filled to capacity.

The first results come from a clean Windows Redstone 3 install compared to a clean Windows 10 Redstone 4 (build 17063), which is a fast ring build including the Meltdown patch:

KASLR-IRQ2.png

The 960 EVO comes in at that same 20% drop seen elsewhere, but check out the 850 EVO's nearly 10% *increase* in performance. The 900P pushes this further, showing an over 15% *increase*. You would figure that a patch that adds latency to API calls would have a noticeable impact on a storage device offering extremely low latencies, but that did not end up being the case in practice.

Since the 960 EVO looked like an outlier here, I also re-tested it using the Microsoft Inbox NVMe driver, as well as by connecting it via the chipset (which uses the Intel RST driver). A similar drop in performance was seen in all configurations.

The second set of results was obtained later, taking our clean RS3 install and updating it to current, which at the time included the Microsoft roll-up 01-2018 package (KB4056892):

KASLR-IRQ2-.png

Note that the results are similar, though Optane did not see as much of a boost here. It is likely that some specific optimizations have been included in RS4 that are more beneficial to lower latency storage devices.

As a final data point, here's what our tests look like with software polling implemented:

KASLR-POLL2.png

The above test results are using an application method that effectively bypasses the typical interrupt requests associated with file transfers. Note that the differences are significantly reduced once IRQs are removed from the picture. Also note that kernel API calls are still taking place here.

Well there you have it. Some gain and some lose. Given that a far lower latency device (900P) sees zero performance hit (actually gaining speed), I suspect that whatever penalty associated with Meltdown could be easily optimized out via updates to the Windows Inbox and Samsung NVMe drivers.