Intel is disabling TSX in Haswell due to software failures

Subject: General Tech | August 12, 2014 - 01:07 PM |
Tagged: Intel, haswell, tsx, errata

Transactional Synchronization Extensions, aka TSX, are a backwards compatible set of instructions which first appeared in some Haswell chips as a method to improve concurrency and multi-threadedness with as little work for the programmer as possible.  It was intended to improve the scaling of multi-threaded apps running on multi-core processors and has not yet been widely adopted.  The adoption has run into another hurdle, in some cases the use of TSX can cause critical software failures and as a result Intel will be disabling the instruction set via new BIOS/UEFI updates which will be pushed out soon.  If your software uses the new instruction set and you wish it to continue to do so you should avoid updating your motherboard BIOS/UEFI and ask your users to do the same.  You can read more about this bug/errata and other famous problems over at The Tech Report.

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"The TSX instructions built into Intel's Haswell CPU cores haven't become widely used by everyday software just yet, but they promise to make certain types of multithreaded applications run much faster than they can today. Some of the savviest software developers are likely building TSX-enabled software right about now."

Here is some more Tech News from around the web:

Tech Talk

Intel Prevents Overclocking of non-K Haswell Processors, and Strips Virtualization and TSX Features From K Parts

Subject: Processors | June 13, 2013 - 09:59 AM |
Tagged: tsx, overclocking, Intel, i7-4770k, haswell

First revealed at IDF Beijing, Intel's latest generation 4th Generation Core "Haswell" processors enjoy a refined architecture, improved processor graphics, an integrated voltage regulator (FIVR), and for the enthusiast crowd, new methods for overclocking.

In truth, the methods for overclocking Haswell are very similar to those used to overclock Intel's Sandy Bridge and Ivy Bridge processors. However, Intel has further unlocked the new Haswell CPUs. Enthusiasts can set an overclocked Turbo clockspeed, use additional base clock (BCLK) values (100 MHz, 125 MHz, and 167 MHz), and overclock the unlocked processor graphics core clockspeed and memory clockspeed (memory in 200 MHz or 266 MHz steps). The additional BCLK values allow for easy overclocks without putting the other subsystems (such as the PCI-E bus, GPU, and memory) out of spec, which is important for the PCI-E bus which needs to be close to 100 MHz for a stable system.

The following PC Perspective articles have further information on overclocking unlocked "K" edition Haswell processors:

Although Intel's overclocking reveal at IDF was fairly detailed, the company did not get into specifics on how overclocking would work on non-K chips.

On that note, the crew over at the Tech Report uncovered some rather disheartening facts such that the non-K edition Haswell processors will, essentially, be locked at stock speeds and not overclockable (they are slightly more locked down than previous generations).

While the K edition Haswell processors, such as the Core i7-4770K, will enjoy unlocked multipliers, unlocked GPU and memory clockspeeds, and additional BCLK options, the standard non-K chips (ie Core i7-4770, Core i5-4670, et al) will have locked multipliers, no Turbo Boost clockspeed overclocking, and will not be allowed to use the additional 125 MHz and 167 MHz BLCK options, which effectively makes overclocking these standard chips impossible. It may still be possible to push the BLCK up a few MHz, but without the extra stepping and gearing ratio options, the other component clockspeeds based off that same base clock are going to go out of spec and will become unstable fairly quickly as you try to push that BLCK up.

There is one saving grace for enthusiasts considering a non-K part, however. The standard non-K CPUs will have Intel's latest TSX extensions and enterprise virtualization technologies enabled.

Although quite the head scratcher, Intel has decided to disable TSX, vPro, and VT-d on the unlocked K edition chips. The TSX extensions are not widely used yet, but will provide a noticeable performance boost to future programs that do take advantage of them by allowing developers to essentially mark off sections of code that can be run independently, and thus increase the multi-threaded-ness of the application by running as much code in parallel across multiple cores as possible. Further, the vPro and VT-d features are used by virtual machine applications (with VT-d being more relevant to the consumer side of things).

In short, Intel has continued to lock down and artificially limit its chips, as many enthusiasts suspected would happen. Standard non-K Haswell processors are more locked down than ever, and even the premium unlocked K CPUs suffer with the (odd) removal of TSX and virtualization support. As Mr. Gasior points out, enthusiasts are going to be faced with an odd choice where they can either spend extra money on a premium K part that will overclock but is limited in other ways, or go with the lower cost part that has all of the ISA extensions and virtualization support turned on... but is not overclockable.

In my opinion, locking down the standard chips is one thing-- Intel needs to incentivize enthusiasts to go with the more expensive (~$25 premium) unlocked K processors some how -- but if those same enthusiasts are spending extra money for a premium chip, they should get all the features the accompanying non-K SKU has as well as overclocking.

What do you think about the artificial limitations placed on the various Haswell SKUs?

Source: Tech Report