Trust No One, Not Even Performance Counters

I can guess why we observe this effect; it’s not like Intel is intentionally messing with us. mfence is a full pipeline flush: it slows code down because it waits for all in-flight instructions to complete their execution. Thus, while it’s flushing that slows us down, the profiling machinery will assign these cycles to any of the instructions that are being flushed. Locked instructions instead affect stores that are still queued. By forcing such stores to retire, locked instructions become responsible for the extra cycles and end up “paying” for writes that would have taken up time anyway.

Assembly Language Optimization Programming

Yosemite’s Mail Drop Considered Harmful

Dan Wood:

If Apple Mail detects a giant attachment, it will offer to send it via Mail Drop, which means that the file is uploaded separately to a temporary iCloud URL. It will stick around for 30 days.

The problem is that if you use this technique, it’s possible that any actual textual message might not be seen by the receiver of the email message.

If you send your email message as plain text — you might not even realize that you are sending a plain text message or a rich text message —or if the receiver’s email client shows them plain text instead of rich text — then ONLY the Mail Drop URL will be seen by the receiver. Not your important message.

Apple Mail FogBugz Mac Mac OS X 10.10 Yosemite Mail Drop