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66 < title > Taming Sparse Rollout</ title >
77 < meta name ="description " content ="Project page for Taming Sparse Rollout: Understanding Stability in RL for Large Language Models with Sparse Attention. ">
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1920 < a class ="brand " href ="#top " aria-label ="Taming Sparse Rollout home ">
20- < img src ="assets/figures/fig-000 .png " alt ="" aria-hidden ="true ">
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2122 < span > Tamed Sparsity</ span >
2223 </ a >
2324 < div class ="navlinks ">
3233
3334 < section id ="top " class ="hero-inner ">
3435 < p class ="eyebrow "> Sparse rollout with Optimal Stability Efficiency Tradeoff for RLVR</ p >
35- < h2 > Taming Sparse Rollout: Understanding Stability in RL for Large Language Models with Sparse Attention</ h2 >
36+ < h2 class ="hero-title ">
37+ < span > Taming Sparse Rollout: Understanding Stability in RL for Large Language Models with Sparse Attention</ span >
38+ </ h2 >
3639 < p class ="authors "> Yang Zhou, Ranajoy Sadhukhan, Zhaofeng Sun, Zhuoming Chen, Souvik Kundu, Saket Dingliwal, Sai Muralidhar Jayanthi, Aram Galstyan, Haizhong Zheng, Beidi Chen</ p >
3740 < p class ="affiliation "> Carnegie Mellon University, Independent Researcher, Intel, Amazon</ p >
3841
@@ -111,7 +114,9 @@ <h2>Taming Sparse Rollout: Understanding Stability in RL for Large Language Mode
111114 < main >
112115 < section id ="desiderata " class ="section visual-band ">
113116 < div class ="section-heading ">
114- < span class ="section-icon "> 1</ span >
117+ < span class ="section-icon section-icon-image ">
118+ < img src ="radom/Telescope.png " alt ="" aria-hidden ="true ">
119+ </ span >
115120 < h2 > Previous Works Limitation and Desirata</ h2 >
116121 </ div >
117122 < div class ="desiderata-layout ">
@@ -163,7 +168,9 @@ <h2>Previous Works Limitation and Desirata</h2>
163168 < section id ="insights " class ="section split full-width-section ">
164169 < div >
165170 < div class ="section-heading ">
166- < span class ="section-icon "> 2</ span >
171+ < span class ="section-icon section-icon-image ">
172+ < img src ="radom/Idea.png " alt ="" aria-hidden ="true ">
173+ </ span >
167174 < h2 > Insights to Sparse to Dense Actor-Policy Mismatch</ h2 >
168175 </ div >
169176 < div class ="wide-grid single-figure ">
@@ -203,7 +210,9 @@ <h2>Insights to Sparse to Dense Actor-Policy Mismatch</h2>
203210
204211 < section id ="control-study-1 " class ="section visual-band ">
205212 < div class ="section-heading ">
206- < span class ="section-icon "> 3</ span >
213+ < span class ="section-icon section-icon-image ">
214+ < img src ="radom/Observation.png " alt ="" aria-hidden ="true ">
215+ </ span >
207216 < h2 > Control Study 1: How Mismatch Threshold Varies to Increasing Model Sizes</ h2 >
208217 </ div >
209218 < div class ="wide-grid ">
@@ -237,7 +246,7 @@ <h2>Control Study 1: How Mismatch Threshold Varies to Increasing Model Sizes</h2
237246 Surprisingly, we make the following finding.
238247 </ p >
239248 < p class ="hypothesis-box ">
240- < strong > Takeaway 1 </ strong > : across a range of model sizes in Qwen3 thinking family, we find that keeping
249+ < strong > Takeaway</ strong > : across a range of model sizes in Qwen3 thinking family, we find that keeping
241250 5-percentile mismatch threshold above 0.86 generally leads to stable RL training, supporting our hypothesis.
242251 </ p >
243252 < p >
@@ -247,29 +256,70 @@ <h2>Control Study 1: How Mismatch Threshold Varies to Increasing Model Sizes</h2
247256
248257 < section id ="control-study-2 " class ="section ">
249258 < div class ="section-heading ">
250- < span class ="section-icon "> 4</ span >
259+ < span class ="section-icon section-icon-image ">
260+ < img src ="radom/GPU.png " alt ="" aria-hidden ="true ">
261+ </ span >
251262 < h2 > Control Study 2: Finding the Lowest Cost given the Mismatch Threshold</ h2 >
252263 </ div >
253264 < div class ="results-layout paired-figures ">
254265 < figure class ="figure-card ">
255266 < img src ="assets/figures/figure106.png " alt ="Qwen3-14B sparse rollout and dense rollout AIME2026 results. ">
256- < figcaption > Qwen3-14B validates stable on-par performance with sparse rollout at the tail threshold .</ figcaption >
267+ < figcaption > From our cost model study, we identified that for block- sparse attention (block-size 16 and above), smaller page size consistently ahead of the tradeoff of distribution alignment to dense and cost .</ figcaption >
257268 </ figure >
258269 < figure class ="figure-card ">
259270 < img src ="assets/figures/figure103.png " alt ="DistillSparse training improves AIME2025 accuracy. ">
260- < figcaption > LoRA distillation can improve alignment and push beyond the plain sparse threshold.</ figcaption >
261- </ figure >
262- </ div >
263- < div class ="metric-strip ">
264- < div > < b > 2.2x</ b > < span > Qwen3-1.7B rollout speedup</ span > </ div >
265- < div > < b > 2.4x</ b > < span > Qwen3-4B rollout speedup</ span > </ div >
266- < div > < b > 2.0x</ b > < span > Qwen3-8B rollout speedup</ span > </ div >
271+ < figcaption > Empirically, we achieve speedup for all different sized models.</ figcaption >
272+ </ figure >
273+ < p class ="full-width-text ">
274+ With the mismatch threshold identified, we then look for the lowest cost achievable while meeting the mismatch threshold.
275+ To make sure our analysis is general and can transfer to different hardware, we use a cost model for our analysis.
276+ </ p >
277+ < details class ="formula cost-model full-width-text ">
278+ < summary > Full explanation of the cost model</ summary >
279+ < p >
280+ We follow Sadhukhan et al. (2025)
281+ and model rollout cost from model size and hardware memory bandwidth. For repeated sampling < code > N</ code > times,
282+ let < code > P</ code > be the number of model parameters, < code > L< sub > in</ sub > </ code > the input prompt length,
283+ < code > L< sub > out</ sub > </ code > the output length, < code > D</ code > the Key/Value dimension, < code > r</ code > the GQA ratio,
284+ and < code > I</ code > one over the GPU SRAM memory bandwidth.
285+ </ p >
286+ < div class ="cost-equation ">
287+ < p class ="formula-label "> Dense attention</ p >
288+ < pre > < code > C< sub > comp</ sub > = 2 * P * N * L< sub > out</ sub > + r * (2 * L< sub > in</ sub > + L< sub > out</ sub > ) * L< sub > out</ sub > * N * D
289+ C< sub > mem</ sub > = 2 * L< sub > in</ sub > * L< sub > out</ sub > * D + N * L< sub > out</ sub > < sup > 2</ sup > * D
290+ C< sub > dense</ sub > = C< sub > comp</ sub > + I * C< sub > mem</ sub > </ code > </ pre >
291+ </ div >
292+ < p >
293+ For block-sparse attention, we assume Top-k kernels incur only minimal overhead for page size
294+ < code > ≥ 16</ code > . With KV budget < code > B</ code > and page size < code > pagesize</ code > , the sparse cost is:
295+ </ p >
296+ < div class ="cost-equation ">
297+ < p class ="formula-label "> Block-sparse attention</ p >
298+ < pre > < code > C< sub > sparse,no scoring</ sub > = 2 * N * P * L< sub > out</ sub > + 2 * r * N * D * B * L< sub > out</ sub > + 2 * I * N * D * B * L< sub > out</ sub >
299+ C< sub > scoring</ sub > = 2 * N * L< sub > in</ sub > * D * L< sub > out</ sub > + (r * N * D * L< sub > out</ sub > < sup > 2</ sup > ) / (2 * pagesize)
300+ + 2 * I * L< sub > in</ sub > * D * L< sub > out</ sub > + (I * N * D * L< sub > out</ sub > < sup > 2</ sup > ) / (2 * pagesize)
301+ C< sub > sparse</ sub > = C< sub > sparse,no scoring</ sub > + C< sub > scoring</ sub > </ code > </ pre >
302+ </ div >
303+ </ details >
304+ < p class ="full-width-text ">
305+ Using this cost model, we find that for < span class ="text-highlight "> block-sparse attention with page size 16 and above</ span > ,
306+ smaller page sizes consistently dominate larger page sizes in the tradeoff between
307+ < span class ="text-highlight "> dense-policy distribution alignment</ span > and cost. In the paper, we provide full details
308+ for other generation-length regimes, and the same conclusion holds across them. Although the cost model does
309+ not explicitly account for < span class ="text-highlight "> Top-k kernel overhead</ span > , our page-size measurements show that when
310+ the Top-k kernels are well implemented, as in Vortex, sparse decoding cost is not highly sensitive to page size.
311+ We therefore use < span class ="text-highlight "> page size 16</ span > for sparsity scheduling, since it gives the strongest
312+ cost-alignment tradeoff while remaining practical for efficient sparse rollout.
313+ </ p >
267314 </ div >
315+
268316 </ section >
269317
270318 < section id ="empirical-generalization " class ="section visual-band ">
271319 < div class ="section-heading ">
272- < span class ="section-icon "> $</ span >
320+ < span class ="section-icon section-icon-image ">
321+ < img src ="radom/iss.webp " alt ="" aria-hidden ="true ">
322+ </ span >
273323 < h2 > Generalization to Larger Model and Other RL domains (Coding RL)</ h2 >
274324 </ div >
275325 < div class ="wide-grid single-figure ">
@@ -295,7 +345,9 @@ <h2>Generalization to Larger Model and Other RL domains (Coding RL)</h2>
295345
296346 < section id ="distillsparse " class ="section ">
297347 < div class ="section-heading ">
298- < span class ="section-icon "> PDF</ span >
348+ < span class ="section-icon section-icon-image ">
349+ < img src ="radom/cosmonautllama.png " alt ="" aria-hidden ="true ">
350+ </ span >
299351 < h2 > DistillSparse: A Technique Pushes for More Aggressive Sparsity and Higher Speedup</ h2 >
300352 </ div >
301353 < div class ="results-layout paired-figures balanced-figures ">
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