Wall Street has changed its tune on Microsoft's search engine

Microsoft's Bing search engine had a good holiday quarter, reporting a 21% year-over-year increase in search revenue when measured in "continuous currency," which removes global market fluctuations.

In a research note, Barclays says Bing will be "a large driver of further services monetization in subsequent quarters."

Microsoft did not break out revenue for Bing specifically, but it did announce last year that Bing was generating $1 billion (£640 million) every three months.

"[Microsoft's] well thought out approach to monetizing search (particularly the bundling of Cortana with Windows 10)" was one of the reason's for Bing's success, according to Barclays.

"[The company's] approach to improve the profitability profile highlights management's disciplined approach to materially improve the financial profile of products over time," the note continues.

Analysts and investors have previously called for Bing, along with Xbox, to be spun out into other businesses while Microsoft focuses on Windows and software services. However, the renewed focus - and revenue - has forced a change in tone.

The man in charge of Microsoft co-founder Paul Allen's money, Paul Ghaffari, told The Financial Times in 2013 that Microsoft needs to "focus on their best competencies" which did not include Bing.

"My view is there are some parts of that operation they should probably spin out, get rid of, to focus on the enterprise and focus on the cloud," said Ghaffari.

However, Microsoft has, under CEO Satya Nadella, made changes to its Bing business. The head of Microsoft's advertising group, Rik van der Kooi, told a group of industry insiders that the company is "all in on search."

Google is still the king of search, but Microsoft has leveraged its other assets - particularly Windows 10 - to drive adoption of the search engine.

Over the past few years Microsoft has grown its search engine share to around 20% in the US. Meanwhile, Google's share has dropped from a peak of 67% in October 2014 to 63% today.

Cortana, the virtual assistant, uses Bing heavily and the software powers Apple's Siri search suggestions, displacing Google.

So, as Satya Nadella put it in a tweet, "Bing IT On!"